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A ALTERAÇÃO DAS ROCHAS ALCALINAS - LAGES - SANTA CATARINA

ALTERATION OF ALKALINE ROCKS - LAGES - SANTA CATARINA

Heinz Peter Lindstaedt (1972)

Adviser: Milton Luiz Laquintinie Formoso

Abstract

In Santa Catarina, northeast from the city of Lages, occurs a domic structure owing to the intrusions of alkaline rocks, with an age of 65 million years.

The alkaline rocks were classified according to their structure in porphiry micro nefeline syenites, phonolites and tinguaites.

A geochemical study of the alkaline rocks showed that they are of the miaskitic type.

The alkaline rocks present two different types of alteration: an incipient alteration characterized by the preservation of the alkaline feldspars and a bauxitic alteration, characterized mainly by the presence of gibbsite.

The factors which control this diferential occurrence of alteration seem to be related mainly to the texture of the original rock and the topography.

Comparative geochemical studies of the main chemical elements as well as of the trace elements on both types of alterations showed a decrease in the grades of SiO2, FeO, CaO, MgO, MnO, Na2O, K2O, and an increase in the grades of Al2O3, Fe2O3, and H2O+ in the bauxitic alteration.

In the incipient type of alteration there is a decrease of Al2O3, Fe2O3, CaO, Na2O, and an increase in FeO, MgO, MnO, K2O and H2O+.

It was also observed that the grades of Zr, Nb, Ga, and V, among the trace elements, showed a notorious increase in the bauxitic alteration.

Chemical comparisons at constant volume over the profile of bauxitic alteration presented a decrease of SiO2, CaO, MgO, Na2O, K2O, and MnO, and an increase in Fe, Al, Ti, and H2O+.

ALGUNS DADOS SOBRE O INTEMPERISMO E A MINERALOGIA DAS ARGILAS DOS BASALTOS E DOS SEUS SOLOS RESIDUAIS

SOME DATA ON THE WEATHERING AND MINERALOGY OF THE BASALTIC CLAYS AND THEIR RESIDUAL SOILS

Breno Corrêa da Silva Filho (1972)

Adviser: Paulo Miranda de Figueiredo Filho

Abstract

This paper deals with the preliminary results of a study concerning the clay mineralogy both of weathered basalts and the soils originated from these rocks. The area in which this work was accomplished is in the municipality of São Valentim, in the State of Rio Grande do Sul. The clay mineralogy study of the rock showed that lightly weathered basalt contains montmorillonite. As the weathering of the rock becomes greater, kaolinite is substituted for montmorillonite. In soils, kaolinite is also the outstanding clay mineral. Chlorite and illite also occur but in very small quantities. The same can be said in relation to gibbsite which is found sometimes in rock samples deeply weathered. Thismineral is also found in some soil samples. Anyway, the occurrence of such a mineral is not important in the area so that kaolinite represents the highest degree of weathering in that region.

On the other hand, samples of a paleo­soil, situated 40 meters below the surface between different lava flows, and taken from underground by drill­holes, have montmorillonite and illite in the clayey material. This fact do not agree with data related to modern soils and calls for quite different climate conditions. According to the factors controlling montmorillonite genesis in soils, that climate must have been of arid or semi­arid type.

DISTRIBUIÇÃO DAS FREQÜÊNCIAS DAS CONCENTRAÇÕES DE ALGUNS ELEMENTOS QUÍMICOS DAS ROCHAS CRISTALINAS E DOS SOLOS DA BACIA DO RIO JAMANXIM, PARÁ

DISTRIBUTION OF THE CONCENTRATION FREQUENCIES OF SOME CHEMICAL ELEMENTS OF CRYSTALINE ROCKS AND SOILS FROM THE JAMANXIM RIVER BASIN, PARÁ STATE

Jaime Simon Almaraz Urdininea (1973)

Adviser: Milton Luiz Laquintinie Formoso

Abstract

This dissertation aims at defining the most representative probability types of the distributions of concentration frequencies in reference to constituent elements (in majority or minority) of the geologic materials, particularly the ones integrating the unaltered rocks and their residual soils.

The collected samples were obtained by means of the field work developed by the author in the Jamanxim River Basin, during 1970­1972, under the auspices of SUDAM (Superintendência do Desenvolvimento da Amazônia). This hydrographic basin is located in the Pre­Cambrian Shield, on the southern border of the Amazon Basin (Itaituba municipality), with an area of 20,800 km² in Pará State, Brazil.

Once determined the adjustable probability functions, this study endeavored to calculate geochemical parameters to be utilized for the lithogeochemical prospection of residual soils.

The probability functions were studied for the following majority oxides and minority elements in dacit riolites, delenites and granitoids: SiO2, Al2O3, K2O, Na2O, CaO, FaO, MgO, MnO, TiO2, Cu, Pb, V, Cr, Co, Ni, Zr, Sr, Sc, Y and Ba; Zn, Cu and Pb were analized from the residual soils of these lithologies (also including the andesitic soils).

Thirteen theoretical distribution functions were tested for each of the above­mentioned populations. These functions were the twelve curves of Pearson's system plus the log­normal function.

ARGILO­MINERAIS EM ROCHAS BASÁLTICAS FRESCAS. MINERALOGIA DOS ESTÁDIOS PRIMÁRIOS DE INTEMPERISMO DE ROCHAS BASÁLTICAS

CLAY­MINERALS IN FRESH BASALTIC ROCKS. MINERALOGY OF THE PRIMARY STAGES OF WEATHERING IN BASALTIC ROCKS

Ari Roisenberg (1974)

Adviser: Milton Luiz Laquintinie Formoso

Abstract

Serra Geral basalts and associated acidic rocks were studied from the mineralogical point of view.

Clay minerals were investigated both in fresh rocks and their incipiently weathered equivalents. Complementary considerations are presented on the geochemistry of the alteration process. Results obtained are related to the geotechnical behavior of these rocks.

The methods used include optical and electron microscopy, X­ray diffraction, isodynamic magnetic separations and staining techniques, besides other technological methods. The samples were collected in the States of São Paulo, Paraná, Santa Catarina and Rio Grande do Sul, and comprise both alteration products from the two top weathered layers and fresh rocks.

The clay minerals in the fresh rocks are of deuteric origin, three reaction mechanisms being mostly responsible for their formation. The newly­formed complex is constituted by an almost constant association of nontronite, montmorillonite, kaolinite (and halloysite), chlorite and interlayered illite­montmorillonite (corren-site). Serpentine only occurs in olivine­bearing rocks. Nontronite is the main clay mineral in basalts and diabases, occurring in amounts equivalent to the interlayered illite­ ­montmorillonite in the acidic differentiates. The isodynamic magnetic separation of minerals allowed a good correlation between the alteration products and their original primary minerals.

Alteration products from rocks subjected to incipient weathering are the same as above plus gibbsite. Serpentine and illite may occur but are of residual origin. The proportions of clay minerals in the alteration products are directly related to the rock type and are similar to those of deuteric origin. Based on the laboratory studies, considerations are made on the relative stabilities of the primary silicates and the newly­formed alteration products.

The geochemical trend is towards increasing removal of elements, except titanium and aluminium; the latter may be leached locally. Potassium is the least mobile of the alkalines and alkaline­earths, owing to the accentuated stability of orthoclase during weathering.

ESTUDO DA ALTERAÇÃO DO ANORTOSITO DE CAPIVARITA, RIO PARDO (RS)

STUDY ON THE ALTERATION OF THE CAPIVARITA ANORTHOSITE, RIO PARDO (RS)

Dione Alves Pintaúde (1976)

Adviser: Milton Luiz Laquintinie Formoso

Abstract

The Capivarita Quadrangle is situated in the northern border of the Uruguay - Rio Grande do Sul shield in the contact area between those crystaline rocks and gondwanic sedimentary rocks. The oldest rocks of this area belong to the Cambaí Group and include migmatites, anorthosites, gneissic syenite and amphibolite. The principal body of anorthosite occurs in a plain (49km²) located in the Capivarita Quadrangle.

Gullies are very conspicuous in the anorthosite plain principally on the hill slopes. The weathering of anorthosite and the development of impermeable argillaceous soils would cause the formation of those gullies. The largest gully is 600m long and 40m wide, where eight soil profiles were studied.

Labradorite (An 52­62) is the most important mineral of anorthosite. A humid temperate climate (annual precipitation: 1635mm; average temperature: 16.6°C) gives good conditions for the chemical weathering of labradorite, which affects directly the minerals of the kaolinite group.

Morphologically the anorthosite soils with A, B, and C sequences are included in the Hydromorphological Brunizem and those with A and A/C sequences as vertisoils.

The minus two micron soil fraction consists of minerals of the kaolinite group (kaolinite, fire­clay and halloysite). In the coarser fractions, plagioclase (98%) and quartz are predominant.

From the base to the top of the soil profile the normative anorthosite decreases a four­fold and the normative albite a three­fold. Kaolinite is the dominant clay mineral increasing a three­fold in the direction of the top of the soil profile. Quartz increases residually and irregularly from the base to the top.

There is a loss of alkaline and earth alkaline elements during the weathering of the anorthosite. Using constant aluminum method, calcium and sodium are leached from the soil profiles, in the amount of 87%. Potassium is anomalous. Iron (+3) increases in the direction of the top, amounting up to 69%. Titanium also increases in the same direction (+1020%).

Calcium is partially retained in calcareous concretions formed in grayish sandy horizons (C1). Plagioclase is almost completely replaced by calcite in these concretions.

With the aid of scanning electron microscopy, the presence of halloysite and fire­clay was observed evidencing the alteration of plagioclase to low cristalinity clay minerals.

Plotting in bidimensional diagram (with log[H4SiO4] and log[Na+]/[H+] as coordinates), analysis of waters in probable equilibrium with anorthosite, it is observed that the composition of those waters are in kaolinite field or in montmorillonite field but very close to the boundary with the former. Therefore, the clay mineral in equilibrium with those waters andwhich normally would be formed is kaolinite. Plotted in the log[H4SiO4] and log[Ca++]/[H+]3 diagram, those waters are situated in the montmorillonite field but close to the boundary line with the kaolinite field. Probably montmorillonite is present in deep contact with anorthosite as it is present in small quantities in the base of the studied profiles.

The alteration of labradorite to kaolinite follows the equation:

Na0,5Ca0,5[Al1,5Si2,5]O8 s,c,lab + 1,5H+aq + 2,75H2Oliq = 0,5Na+aq + 0,5Ca++aq + H4SiO4aq + 0,75Al2SiO2O5(OH)4 s,c,kaol

labradorite = kaolinite

The low pH makes the weathering of the labradorite easier.

Tridimensional diagram, using log[Na+], log[H4SiO4] and log[Ca++]/[H+]3 as coordinates, shows a plane dividing the fields of kaolinite (internal field) and labradorite (external field). Decrease of log[Na+], log[H4SiO4] and log[Ca++]/[H+]3 facilitates the alteration of labradorite to kaolinite.

Strontium changes from 1020 to 70ppm from the base to the top of profiles. Strontium has a similar behavior to calcium during the weathering of anorthosite. Even in calcareous concretions, which are formed in C soil horizon and indicate the leaching of calcium, strontium behaves as calcium. The correlation coeficient between these two elements in the profiles is +0.91.

ESTUDO GEOQUÍMICO DE SOLOS APLICADO À PROSPECÇÃO DE MINERALIZAÇÕES CUPRÍFERAS NA REGIÃO DE BAGÉ - CAÇAPAVA DO SUL, RS

GEOCHEMICAL STUDY OF SOILS, APPLICABLE TO THE PROSPECTION OF COPPER MINERALIZATIONS IN BAGÉ - CAÇAPAVA DO SUL REGION, RS

Lauro Valentim Stoll Nardi (1978)

Adviser: Milton Luiz Laquintinie Formoso

Abstract

The purpose of the present dissertation is the characterization of some geochemical parameters related to the dispersion of copper, lead, nickel, cobalt, vanadium, zirconium and gallium in soils and its applicability in the geochemical prospecting for copper and lead mineralizations.

The area pesently studied is located in the municipality of Bagé, State of Rio Grande do Sul, and is constituted by sedimentary and migmatitic rocks cut by quartz veins with pyrite, chalcopyrite and locally galena and silver mineralizations.

With this purpose in mind, data related to the concentrations of copper, nickel, cobalt, lead, vanadium, gallium, zirconium, zinc, magnesium, manganese, free­iron, organic matter and cold extractable copper and zinc were interpreted.

Data processing involved application of basic statistical techniques such as: measures of central tendency, dispersion, tests of significance, correlation and moving average.

The most important conclusions are:

- geochemical prospecting in soils may be used reliably for detecting copper and lead mineralizations, under the conditions herein studied, even in the case of small low grade mineralizations;

- the occurrence of these mineralizations is indicated in soils through variations in the concentrations of copper or lead, or in Cu/Ni ratios;

- total metal determinations yield better results than partial extraction techniques;

- the hydrated oxides of iron and manganese, particularly of the latter element, are the main carriers of copper, nickel, cobalt and vanadium in soils;

- pH, organic matter, and clay minerals have only a secondary role in the geochemical mobility of the studied elements;

- the background of copper in soils corresponds to that determined in other areas in Brazil and shows values similar to those obtained for the parent rocks.

ESTUDO PETROLÓGICO E GEOQUÍMICO DOS CARBONATITOS DA FAZENDA VARELA, LAGES, SANTA CATARINA, BRASIL

PETROLOGICAL AND GEOCHEMICAL STUDY OF THE CARBONATITES FROM FAZENDA VARELA, LAGES, SANTA CATARINA, BRAZIL

Luiz Fernando Scheibe (1979)

Adviser: Milton Luiz Laquintinie Formoso

Abstract

The Fazenda Varela carbonatites are the first described occurrence in association with the alkaline rocks of the Lages Dome, Santa Catarina State, Southern Brazil. They are located near the center of the alkaline complex, with approximate geographic coordinates 29°39'S and 50°17' W.G.

These carbonatites are brecciated and heterogeneous, and the main constituents are ankerite, barite, orthoclase, synchisite and pyrite; pyrochlore and monazite are present in some cases. Quartz and apatite are secondary minerals and magnetite in blocks is also present. The carbonatites are white, turning to brown when weathered. Final weathering products are ferralitic crusts and soils rich in barium, iron, manganese, and thorium.

The carbonatites intruded the sandstones and siltstones of the Rio Bonito Formation, producing extensive feldspathization with potassic character.

The mineral composition, the high Ba/Sr, Nb/Ta and Th/U ratios, and the high total and relative concentration of the light lanthanides indicate that the Fazenda Varela carbonatites are representatives of the last phases of a fractionation proccess. Carbon and oxygen isotopic ratios as well as the geologic setting indicate sub­volcanic emplacement, but the value of the Sr87/Sr86 ratio is compatible with a mantle origin, perhaps affected by little crustal contamination or by the high potassium concentration of the fenitizing fluids.

The indications obtained by the present study suggest the possible occurrence of a larger body of carbonatitic rock, at a level below the present erosion surface, representing the early phases of crystallization of the carbonatitic magma.

CONTRIBUIÇÃO AOS ESTUDOS PETROLÓGICOS, GEOQUÍMICOS E METALOGENÉTICOS DA OCORRÊNCIA CUPRÍFERA DE CERRO DOS ANDRADAS, CAÇAPAVA DO SUL, RS

CONTRIBUTION TO THE PETROLOGIC, GEOCHEMICAL AND METALOGENETIC STUDIES ON THE COPPER MINERALIZATION IN CERRO DOS ANDRADAS, CAÇAPAVA DO SUL, RS

Sandra Maria de Arruda Furtado (1980)

Adviser: Milton Luiz Laquintinie Formoso

Abstract

The results of the study on the copper mineralization of Cerro dos Andradas, Rio Grande do Sul, Southern Brazil, are presented and discussed. Sulphides occur in schists of the Vacacai Formation of Precambrian age.

The lithologies of the area comprise: (1) a sequence of parametamorphic rocks constituted mainly by chlorite and/or phengite; (2) partially to completely metamorphosed andesitic lava flows, and (3) ultramafic rocks composed of talc, serpentine, chlorite, and dolomite.

Mineral assemblages indicate a relatively high pCO2 during metamorphism and metamorphic conditions of the greenschists facies (chlorite zone).

Two intersecting schistosities and a cataclastic foliation have been observed.

The copper mineralization is distributed over three irregular bodies with disseminated ore minerals. The ore is dominantly constituted by chalcocite, subordinately bornite, pyrite, and chalcopyrite, and rarely digenite, covelite and native copper. A maximum of 15 ppm of silver has been detected.

The oxidation of the ore is observed to a depth of 30 meters through the occurrence of malachite and brochantite.

The primary ore minerals show evidence of some mtamorphic conditions as the enclosing schists. The origin of the ore is discussed.

PETROLOGIA DO COMPLEXO PALMA, RIO GRANDE DO SUL

PETROLOGY OF THE PALMA COMPLEX, RIO GRANDE DO SUL

Marco Antônio Maurer Garcia (1980)

Adviser: Milton Luiz Laquintinie Formoso

Abstract

The purpose of the present dissertation is to study a geologically controverted region, with respect to its geotectonic significance and age.

The area is located in São Gabriel, State of Rio Grande do Sul, and comprises folded, faulted and metamorphosed sedimentary and igneous rocks. These are metasediments of the flysch facies, granite, metadacites, metabasalts, metagabbros, metaperidotites, metapiroxenites and serpentinites, with a possible spinifex texture. The name Palma Complex is proposed for this association.

Petrographic, structural and geochemical studies led to the following important conclusions:

1. The petrograpahic data showed both a cummingtonite + talc paragenesis and the presence of ferrit­chromite, which characterizes, at least, an epidote­anphibolite metamorphic facies for the Complex;

2. The existence of 3 events of deformation;

3. The affiliation of the metavolcanic sequence, where metadacites are included, is calc­alkaline;

4. The possibility that the Palma Complex may represent a greenstone belt is suggested by petrographic association and chemical parameters.

COMPLEXO BÁSICO­ULTRABÁSICO DE PEDRAS PRETAS, RIO GRANDE DO SUL - ASPECTOS PETROLÓGICOS E GEOQUÍMICOS

BASIC­ULTRABASIC COMPLEX OF PEDRAS PRETAS, RIO GRANDE DO SUL - PETROLOGICAL AND GEOCHEMICAL ASPECTS

Inês Terezinha Soares Fernandes do Rêgo (1980)

Adviser: Milton Luiz Laquintinie Formoso

Abstract

The Basic­Ultrabasic Pedras Pretas Complex is tectonically situated, with the aspect of a mega­ ­xenolith, in the southern part of the São Sepé Granitic Complex, located in São Sepé, Rio Grande do Sul State. It comprises a small area (2.55km²) and is composed of basic and ultrabasic rocks metamorphosed to medium­ and low­grade, with largely preserved original structures, textures and mineralogy. Based on petrographical and geochemical features, basic and ultrabasic units can be individualized. Within these units, lithologic types moderately differentiated are observed, although they cannot be mapped. The basic unit comprises gabbros, leuco­ -gabbros and anorthosites, and the ultrabasic unit comprises rocks with approximately dunitic, peridotitic, pyroxenitic, gabbroic and anorthositic composition, with serpentinites and serpentinized equivalents.

Layering, stratifications and igneous laminations are noticeable. The petrological and geochemical features of the Pedras Pretas Complex are compatible with the classic model of formation of magmatic lithologies by cumulative processes in stratiform complexes. The chemical characteristics of the basic unit indicate tholeiitic affinities, similar to the differentiation trend of the typical stratiform complexes, with moderate iron enrichment.

Radiometric dating has not yet furnished conclusive data. Nevertheless, K/Ar 800­1000 m.y. values indicate that the Pedras Pretas Complex is of Pre­Brazilian age.

CONTRIBUIÇÃO AO ESTUDO DA FORMAÇÃO GRAXAIM DO CENOZÓICO DA PLANÍCIE COSTEIRA DO RIO GRANDE DO SUL

CONTRIBUTION TO THE STUDY OF THE GRAXAIM FORMATION OF THE CENOZOIC OF THE COASTAL PLAIN OF RIO GRANDE DO SUL

Lúcia Ayala (1980)

Adviser: Milton Luiz Laquintinie Formoso

Abstract

The Graxaim Formation, chiefly composed of arkosic sandstones, occurs along the coastal plain of the Rio Grande do Sul State, Brazil, cropping out as a broad NE­SW - trending strip, which covers about 9,945km² and is located immediately west of the State's lagoonal system. It extends from surroundings of the town of Jaguarão, in the south, to the neighbourhoods of Guaíba, in the North.

The Graxaim Formation is the oldest Cenozoic formation in Rio Grande do Sul State. It crops out immediately west of the cited lagoonal system and dips east below the younger units, towards the centre of the Pelotas Basin.

The outcropping portion of the Formation lies directly on its source­area, the Pre­Cambrian igneous and metamorphic rocks that constitute the "Sul Rio­grandense- ­Uruguaio" Shield.

Mainly composed of sandstones, the unit presents subordinated silty­argillaceous and areno­ ­conglomeratic facies, the first slightly predominating in relation to the latter.

During the Graxaim deposition times, there has been an alternation of dry and humid climates, which imprinted their characters in the development of the unit.

Composed of clastic material deposited by streamfloods and sheetfloods, that run eastward from the uplands of the shield to nearby lowlands, the Graxaim Formation is made up of a series of alluvial fans that, interfigering in space and superposing themselves in time, gave origin to the constant and repetitive vertical and horizontal faciological changes of this stratigraphic unit.

CONTRIBUIÇÃO À GÊNESE DAS OCORRÊNCIAS CUPRÍFERAS ESTRATIFORMES DE CERRO DOS MARTINS, RS

CONTRIBUTION TO THE GENESIS OF THE STRATA­BOUNDED COPPER OCCURRENCES IN CERRO DOS MARTINS, RS

Juan Antonio Flores Altamirano (1981)

Adviser: Milton Luiz Laquintinie Formoso

Associated Adviser: Marcelo José Ribeiro

Abstract

This dissertation describes strata­bounded copper outcrops associated to gray siltstones and sandstones, that occur in the Northern part of the Cerro dos Martins area, Caçapava do Sul (RS), Brazil.

The Companhia Brasileira do Cobre obtained the legal rights to develop a prospection project in the studied area.

The geology consists of beds of siltstones, sandstones and conglo-merates, alternated with andesites, in a vulcano­sedimentary environment. Andesites to rhyolites also occur as hypabissal bodies that cut discord-antly the layered sequence.

The results show, in the mineralized interval, an epigenetic character for the copper ore, related to the diagenic evolution of the sequence, fairly close to the reducing levels of framboidal pyrite, responsible for the trapping environment.

The andesite fragments in the clastic rocks cause the element zonation, determinated by copper in the bottom position, lead and zinc in the top of the sedimentary sequence.

The X­Ray studies show the predominance of illite and chlorite in the clay fraction, indicating diagenesis and anchimetamorphism in the illite - chlorite facies.

The geostatistic results demonstrate a low correlation between copper and the other trace elements, what enforces the epigenetic nature of the strata­bounded copper mineralization.

PETROLOGIA DO MACIÇO MÁFICO­ULTRAMÁFICO PASSO DO IVO, SÃO GABRIEL, RIO GRANDE DO SUL

PETROLOGY OF THE MAFIC­ULTRAMAFIC PASSO DO IVO MASSIF, SÃO GABRIEL, RIO GRANDE DO SUL

Marisa Terezinha Garcia de Oliveira (1981)

Adviser: Milton Luiz Laquintinie Formoso

Associated Adviser: Leo Afrâneo Hartmann

Abstract

The Mafic­Ultramafic Passo do Ivo Massif, which is located to the south of São Gabriel (RS), is an elongate body associated with Vacacaí Group, metamorphites and fault­ ­bounded by granitic rocks.

The following zones of preferential concentration of minerals were identified: olivine cumulates, clinopyroxene­olivine cumulates, clinopyroxene­ortho­pyroxene­olivine cumulates and gabros.

The mineralogy and textures are well preserved in the core of the body. On the outer portions, metamorphic minerals predominate, including actinolite, chlorite, tremolite, and cummingtonite. Petrographic studies showed cumulate textures, typical of stratiform complexes. Chemical analyses indicated that MgOand Fe2O3 have negative correlation with SiO2, wehereas FeO, TiO2, Na2O, CaO, and Al2O3 have positive correlation with SiO2. Cr, Ni and Co contents average 4288 ppm, 656 ppm and 175 ppm, respectively, in the ultramafites. It is inferred that the body was formed through fractional crystallization of mafic minerals from a tholeiitic magnesian magma of komatiite affinity. After the emplacement of the mafic­ultramafic body into the metamorphites, the surrounding granites were intruded. Contact metamorphism in the massif attained the greenschist and locally amphibolite­facies. The magnesian schists, present in a few locations within the massif, were probably formed during the strong NE­trending faulting that affected the area.

CARACTERÍSTICAS GEOLÓGICAS E TECNOLÓGICAS DO CARVÃO DA REGIÃO DE RESERVA (PR)

GEOLOGICAL AND TECHNOLOGICAL CHARACTERISTICS OF THE COAL FROM RESERVA REGION (PR)

Paulo Sérgio Gomes Paim (1981)

Adviser: Zuleika Carreta Corrêa da Silva

Abstract

The macro and microscopic characteristics and chemical composition of coals from Paraná State showed that they differ from humic coals.

Thinny banded coal with abundant to predominant vitrain predominate northward in the area (Marins­Marçal). Vitrinite (colinite) predominates, followed by exinite (mainly sporinite and alginite), clay­minerals and pyrite.

Data from ultimate analyses showed H/C and O/C atomic ratios, which characterize the material between kerogen types II and III. Results from organic geochemistry analysis present peaks in both high­carbon numbered (C23-C27) and low­carbon numbered (C14­C17) n­alcanes.

Petrographic and chemical characteristics, associated with palynological studies, suggest that the peat­forming plant association developed between forest­swamp and subaquatic facies, in Teichmüller's concept, or was formed in a shrub­swamp in a limnotelmatic environment, according to Hacquebard and Donaldson.

Thynny banded coal with moderate to sparse vitrain predominate southward in the area (Remanso­Morro Chato). Clay minerals are dominant and microscopically associated with decreasing amounts of alginite, colinite, inertodetrinite and vitrodetrinite, accordingly.

Petrographic and palinogical data suggest either a subaquatic facies, according to Teichmüller, or a limnic open­moor facies, according to Hacquebard and Donaldson.

High contents of pyrite, predominantly framboidal­shaped, presented by coal seams from both studied areas, pointed out to a possible influence of sea water.

The close association of organic and inorganic material is due to palaeoenvironmental characteristics: near­shore conditions and organic facies.

The degree of coalification was estimated by Randon reflectance of vitrinite, volatile matter of vitrite, carbon content and calorific value of total coal. Therefore, the coal seams were classified as High­Volatile Bituminous Coal C to B (ASTM) or as 'Braunkohle' / 'Steinkohle', according to the German classification.

The high sulfur content unables the coals to be used in the industry without a previous systematic cleaning process.

Although the sulfur can be reduced to 50% of the initial content, as showed by densimetric process, the final amounts are still high. The separation of inorganic constituents from organic matter is very difficult because of the close association of both components. There are three main possible industrial uses that should be analyzed: direct combustion, gasification and pyrolise, which are dependent upon the amount of available coal and the cleaning of sulfur.

MINERALOGIA, PETROGRAFIA E GEOQUÍMICA DO COMPLEXO ULTRAMÁFICO DE SERRINHA, SÃO GABRIEL, RS

MINERALOGY, PETROGRAPHY AND GEOCHEMISTRY OF THE ULTRAMAFIC SERRINHA COMPLEX, SÃO GABRIEL, RS

Helem Maria Vieira (1981)

Adviser: Milton Luiz Laquintinie Formoso

Abstract

This dissertation comprises the detailed study of the Serrinha Ultramafic Complex, located in São Gabriel, RS. Forty samples were studied, comprising thirty serpentinites and ten magnesian schists; the latter constitute the borders of the complex. Several techniques were used for mineralogical determinations, particularly petrography, X­ray diffraction and scanning electron microscopy. Three serpentine varieties were identified, namely chrysotile, lizardite and antigorite, presenting several textural patterns, both pseudomorphic (mesh, curtain and bastite) and non­pseudomorphic (interlocking and interpenetrating). Chlorite was determined as clinochlore. The border schists are constituted by talc and tremolite in different proportions, chlorite, carbonate, and very small amounts of opaque minerals. Slightly different mineralogy was observed in one smalloutcrop in the southern portion of the serpentine body, corresponding to tremolite, partly serpentinized olivine, carbonate and chlorite.

Ten samples were analyzed for major elements, using conventional chemical techniques, and about fifty samples for minor elements using emission spectrography. Major­ ­element contents agree with the values expected for the types of rocks involved. Nevertheless, SiO2, Al2O3 and CaO were probably remobilized during serpentinization, concentrating in the border schists. The minor elements Cr, Co, Ni, Cu, V, and Mn have contents typical of ultramafic rocks. The results suggest that the serpentinite was formed from an olivine + diopside peridotite, submitted to progressive metamorphism in the greenschist or anphibolite facies and later to retrometamorphism in the greenschist facies.

GEOLOGIA DA REGIÃO DE PALMA, SÃO GABRIEL, RIO GRANDE DO SUL

GEOLOGY OF THE PALMA REGION, SÃO GABRIEL, RIO GRANDE DO SUL

Farid Chemale Júnior (1982)

Adviser: Léo Afraneo Hartmann

Abstract

The geology of the Palma Region is rather complex, with several lithostratigraphic units. The Palma Complex is one of these, containing closely related meta­sedimentary, acid to basic meta­igneous and ultramafic rocks. The Lageado meta­granite has a quartz­dioritic to sienogranitic composition and presents concordant foliation and metamorphism with respect to the Palma Complex. Both units were affected by greenschist to lower amphibolite­fácies metamor-phism. The stratiform Passo do Ivo Mafic­ultramafic Massif is closely related to the Palma Complex. The Lagoa da Meia Lua Granite has a dioritic to granodioritic composition and a pre­Brasiliano Cycle age.

Brasiliano Cycle granitoids are present, intruded into cratonized older rocks. Eo­paleozoic dykes can also be found, together with Paraná Basin sedimentary rocks and diabases.

Petrochemical studies show that the Palma Complex meta­ultramafites and the Passo do Ivo mafic­ultra-mafic rocks have komatiitic affinity. The acid to basic rocks show calco­alkaline trends. These rock types in addition to the meta­ ­sediments, show characteristics similar to low­grade greenstone­ ­granite terrains.

PROSPECÇÃO GEOQUÍMICA APLICADA À PESQUISA DE SULFETOS NÃO­AFLORANTES, ASSOCIADOS A ROCHAS SEDIMENTARES EOPALEOZÓICAS NA REGIÃO DA FAZENDA SANTA MARIA, CAÇAPAVA DO SUL, RS

GEOCHEMICAL PROSPECTION APPLIED TO THE RESEARCH OF NON­OUTCROPPING SULPHIDES ASSOCIATED WITH EARLY PALEOZOIC SEDIMENTARY ROCKS OF THE FAZENDA SANTA MARIA REGION, CAÇAPAVA DO SUL, RS

Otávio Augusto Boni Licht (1982)

Adviser: Marcelo José Ribeiro

Associated Adviser: Adolpho José Melf

Abstract

The geochemical prospecting work presented here was carried out on the Sul­rio­grandense Shield, Southern Brazil, near the copper Mines of Camaquã, in a place called Santa Maria Farm, by following a sedimentogenic model for the mineralization, over a sedimentary clastic sequence ("Bom Jardim" Group) of Late Pre­Cambrian age.

The sampling was performed by using stream sediments (146 samples on the reconaissance phase and 135 samples on the detail phase), soils (3,299 samples), outcropping rocks (1,735 samples) and core samples (about 2,000 samples).

The analytical procedure used atomic absortion spectrometry for the determination of Cu, Pb, Zn, Feand Mn, and X­ray diffraction for determination of clay minerals.

The statistical procedure for the analytical data was developed by using probability graphs which were interpreted following Lepeltier (1969).

The results pointed out stratiform and sub­horizontal deposits of Pb­Zn ores, at 60 meters below surface, hosted by clastic sedimentary rocks, with a play of colours grading from white to gray.

The ore reserves on the Area 2 deposit reaches at 13,500,000 tonnes with a grade of 0.92% Pb and 1.24% Zn; and the Area 3 ore deposit amounts 30,000,000 tonnes with a grade of 1.53% Pb and 0.76% Zn.

MINERALIZAÇÃO DE CHUMBO E ZINCO EM ARENITOS DO DISTRITO DE CAMAQUÃ, RS

THE Pb­Zn MINERALIZATION IN SANDSTONES OF THE CAMAQUÃ DISTRICT, RS

Waldemar Salomão Rodrigues Badi (1983)

Adviser: Hardy Jost

Abstract

The Pb­Zn sandstone type mineralization of the Santa Maria deposit, Southern Brazil, was discovered in 1978 by geochemical exploration and drilling. The deposit is located in a sedimentary pile of probable Upper Proterozoic to Cambrian age, belonging to the lower mollasses of the central region of the State of Rio Grande do Sul basement area.

The sedimentary rocks of the Santa Maria deposit are mostly white arkosic sandstone, interlayered with minor conglomerates and rare siltstones. The rudites and arenites (Vargas Member, Arroio dos Nobres Formation) are arranged in a large and thick deltaic system. The coarse­ ­grained deltaic system grades laterally into and progrades vertically on very fine­grained, deep water rythmites of the Mangueirão Member of the same major stratigraphic unit. NE shear zones, NW tensional faults, diabase dikes, and joints are the most important post­depositional features, but they do not imprint major dislocations as to introduce difficulties during correlations within the deltaic system.

The geology of the mineralization is described for the first time. Paleogeographic, paleohydrologic and lithologic controls for ore emplacement, situation and geometry of the deposit, its mineralogy, paragenesis, succession and the effect of diagenesis, ore textures and structures as well as a discussion about its genesis are presented. Available information has been obtained from drill­holes, since minning operations have not begun to expose the ore.

The stratigraphic unit where the ore occurs is strongly controlled by paleogeographic features. A volcano­ ­plutonic mainland bordered by narrow foredeeps is the model proposed. The ore was emplaced within sequences denoting main clastic feeding channels, which are also characterized by rock assemblages with fast lateral and vertical facies change, and low carbonate content. The metals probably were deposited from brines flowing through the stratigraphic sequence during compaction and following the migration of hydro-carbons.

The geometry of the deposit is complex. It crosscuts the stratigraphy of the sandstone­conglomerate assemblage. Geometry can be focused from the standpoint of the metalic zonality and of the geometry of the sedimentary host rocks. Zonality is rather strong and marked by Cu­Pb­Zn ordered from conglomerates to very fine­grained sandstones. The morphologic effect of the sedimentary framework upon ore is represented by the termination of the mineralization along zones of facies change.

The mineralogy of the deposit is simple. Pyrite, galena, sphalerite, rare chalcopyrite, and native silver occur in arkosic sandstones and in the arkosic matrix of conglomerates. Textural and structural evidences suggest that the sulfides and native silver were deposited as a part of the diagenesis and cementation of the sedimentary pile. Major cementing materials comprise authigenic quartz and albite, sulfides, illite, and carbonates (calcite and ankerite/siderite). Illite crystalinity index suggests that sulfide deposition took place probably under advanced diagenesis. Mineralized intraclasts, which occur in barren conglomerates, suggest that brine flow, cementation, and consolidation of individual strata took place in successive flushes before the definite closure of the sedimentary process.

The Santa Maria Pb­Zn sandstone­type deposit is similar to other deposits of the category of Upper Proterozoic­Cambrian age, but its stratigraphic close association with copper deposits of the Cu sandstone type opens new perspectives for the study of regional metal zonation in an overall rudite­arenite sulfide ore deposit typology.

EVOLUÇÃO PALEOAMBIENTAL E TECTÔNICA DA BACIA DO CAMAQUÃ (RS): UMA INTRODUÇÃO

PALAEOENVIRONMENTAL AND TECTONIC EVOLUTION OF THE CAMAQUÃ BASIN (RS): AN INTRODUCTION

Antônio Romalino Santos Fragoso César (1983)

Adviser: Hardy Jost

Associated Adviser: Renato Rodolfo Andreis

Abstract

The Camaquã Basin is a molassic through (Southeastern Foredeep) which borders the Dom Feliciano orogenic belt, in the Rio Grande do Sul shield, and separates this belt from the Rio de La Plata craton at northwest. The Camaquã basin is an elongated (NE­SW) tectonic basin with maximum width of 65km and outcropping length of 160km; it is predominantly filled with imature clastic sequences, and presents locally a thickness of more than 4,000m.

During its evolution, from the Late Proterozoic (Vendian) to Early Phanerozoic (Cambro­Ordovician), it revealed a radical change in depositional environment­from deep sea (submarine fans and associated turbidites) to transitional (coastal fans and shallow water sandstones) and continental conditions ("piedmont", fluviatile, lacustrine and eolian deposits). These environmentalchanges reflected several phases of its tectonic evolution: during the transitional stage of the Brasiliano Cycle, initiated with the Molasse Synclinoria phase (deep and shallow water deposits); followed by a Tectonic Imbrication phase, characterized by tectonic slivers of the marine deposits imbricated in the basement and covered by syntectonic ruditic fans; and culminating in a Graben phase, with reactivation of the NE­SW (and a subsidiary NW­SE) system of regional faults, and the formation of continental basins under arid or semi­arid climatic conditions.

This dissertation proposes a stratigraphic model to the sedimentary units of the Camaquã Basin, with a preliminary subdivision into three formations: Arroio dos Nobres, Vargas and Guaritas, each one with proper lithologic characteristics and specific paleoenvironmental and tectonic significance.

PETROLOGIA E GEOLOGIA ECONÔMICA DE GRANITÓIDES NA REGIÃO CAMPINAS­FIGUEIRAS, RS

PETROLOGY AND ECONOMIC GEOLOGY OF GRANITOIDS IN THE REGION OF CAMPINAS­FIGUEIRAS, RS

José Carlos Frantz (1983)

Adviser: Hardy Jost

Abstract

Granitoids (Campinas Granite) with tin mineralization in the Encruzilhada do Sul region, southern Brazil, are known since the beginning of this century, but the magmatic processes and their influence on the formation of ore have not been discussed yet.

The Campinas Granite occurs as four stocks intruded into granits of the Encruzilhada Complex and schists of the Porongos Suite along the contact between the two units, which is marked by a large scale, deep­seated transcurrent lineament.

The modal composition of the studied stocks is that of a quartz monzonite with their chemical composition showing that they build up a line of differentiated, individually homogeneous granodiorites.

The high Sr87/Sr86 ratio and the recognition of inherited mineral phases from source rocks suggest that the granitoid magmas resultedfrom crustal partial melting. Their peraluminous nature, which results in normative corundum, and the textural characteristics of the magmatic phases indicate a rapid crystallization, probably owing to the degasification of the magmas.

The release of the volatile phase was not only responsible for the metal depleation in the stocks but also for the widespread hydrothermal alteration halos (kaolinization, muscovitization, turmalinization, greisenization) with cassiterite­bearing quartz veins.

Circulation of solutions within country rocks was mostly facilitated by the milonitic foliation in those stocks, whose intrusion was controled and took place within the main milonite zones. Larger intrusions at the milonite margins show intraplutonic mineralization because of the trapping of solutions at the apex of the cupules.

GEOLOGIA, PETROLOGIA E ESTRUTURA DOS METAMORFITOS DA REGIÃO DE CAÇAPAVA DO SUL, RS

GEOLOGY, PETROLOGY AND STRUCTURE OF THE METAMORPHITES FROM THE CAÇAPAVA REGION, RS

Maria de Fátima Aparecida Saraiva Bitencourt (1983)

Adviser: Léo Afraneo Hartmann

Abstract

The Caçapava do Sul region is described as a sequence of polymetamorphic rocks designated Passo Feio Metamorphic Complex, bordering an association of granitic rocks named Caçapava do Sul Granitic Complex. The metamorphic rocks comprise mainly metapelites, amphibole­bearing schists and gneisses, metagabros, and meta­volcaniclastic rocks, and, in smaller proportions, magnesian schists, quartzo­feldspathic gneisses, marbles, quartzites, and metavolcanics. Small diabase and lamprophiric dikes intrude these rocks. A gradational relationship is observed between foliated and massive anchimetamorphic rocks, coinciding with the predominance of meta­volcaniclastics over metapelites. Two regional metamorphic events are recognized. The first reached the staurolite zone of the amphibolite facies; the occurrence of andaluzite is suggestive of low­pressureconditions. The second event is a retrogressive, greenschist facies metamorphism, having reached the biotite zone. Three folding episodes are described. The second originated the main foliation, S2, and the last one built up the regional antiformal stgructure, by the folding of S2. The granitic rocks constitute the core of the regional structure and it is suggested that this complex of rocks, or part of it, has been affected by the second episode of folding and metamorphism. The geochemical study of amphibole­bearing rocks indicates that their trace element content, mainly that of Cr, Co, and Ni, is characteristic of igneous rocks. However, imperfect correlations with igneous differentiation trends are observed as well as the presence of mixed trends, towards argillaceous sediments. It is concluded that such rocks were provided partly by igneous rocks and partly by reworked volcanics and pyroclastics.

O COMPLEXO VULCANO­SEDIMENTAR­ULTRAMÁFICO E GRANITÓIDES DA REGIÃO DE IBARÉ, RS

THE VOLCANO­SEDIMENTARY­ULTRAMAFIC COMPLEX AND GRANITOIDS OF THE IBARÉ REGION, RS

Márcio Paulo Naumann (1985)

Adviser: Léo Afraneo Hartmann

Abstract

This dissertation deals with the petrological, geochemical, and geochronological study of some Pre­Cambrian units, occurring in the Ibaré region, RS. The name Ibaré Complex is proposed for ultramafic and metavolcano­sedimentary lithologies. This complex comprises the Bela Vista Sequence, which contains metarkoses, iron formations, metagreywackes, metarhythmites, metapelites, metabasites and metandesites, and the Corticeira Sequence, with serpentinites, magnesian schists, mafic hornfelses, rodingites, chloritites and tourmalinites. Two regional metamorphic events were recognized. The first and most intense reached the chlorite zone of the greenschist facies. Contact metamorphism was locally developed reaching the hornblende hornfels facies. Three deformation episodes were identified: thefirst originated the main foliation, which was folded during the subsequent episodes. Intrusive granitoids are related to tectono­magmatic events of Upper Proterozoic to Eo­Paleozoic ages. They comprise three distinct groups of magmatic rocks represented by the Timbaúva Granodiorite, Santa Rita Monzogranite and the Jaguari Intrusive Suite. Petrochemical studies show that the metagreywackes and metarhythmites of Bela Vista Sequence have volcanogenic affiliation. In the same way, the ultramafic rocks show komatiitic affinity. The chemical composition of the minerals was determined by electron­probe analysis of granitoids an mafic­ultramafic hornfelses. Isotopic studies of the Timbaúva Granodiorite and of the tremolitites of the Corticeira Sequence have been carried out.

PETROLOGIA E GEOQUÍMICA DO VULCANISMO MESOZÓICO DE JAGUARÃO - RS

PETROLOGY AND GEOCHEMISTRY OF THE MESOZOIC VOLCANISM OF JAGUARÃO - RS

Nelson Vieira Júnior (1985)

Adviser: Milton Luiz Laquintinie Formoso

Associated Adviser: Ari Roisenberg

Abstract

The mesozoic volcanic sequence that occurs in the region of Jaguarão (Rio Grande do Sul State - Brazil), covers an area of aproximately 160km² and is composed of glassy dacites and rhyodacites. This sequence overlies the crystalline basement that consists of granitic rocks, schists and quartzites, which correspond to the xenoliths found very often in the volcanic rocks. The main crystalline phases consist of plagioclase and hypersthene. The plagioclase phenocrysts and xenocrysts contain glassy inclusions produced by partial melting processes.

Magmatic modelling using major and trace elements, has demonstrated that these volcanics could not have derived from a primary basaltic magma by processes like fractional crystallization, assimilation/contami-nation of fractional crystallization plus assimilation. On the other hand, incompatible elements ratios, Sr87/Sr86 initial ratios and the slope of REE patterns, suggest an origin by crustal melting.

Petrochemical, petrographic and stratigraphical data reveal that these volcanics are entirely distinct from the Serra Geral Formation. This justifies the introduction of a new lithostratigraphic unit, named Jaguarão Formation. This formation is probably associated with the Lagoa Mirim Marginal Basin, representing one of the oldest volcanic eruption related to the Atlantic Ocean opening.

PETROQUÍMICA E PROSPECÇÃO LITOGEOQUÍMICA DA ÁREA DE MERITA, REGIÃO DE VOLTA GRANDE, LAVRAS DO SUL, RS

PETROCHEMISTRY AND LITHOGEOCHEMICAL PROSPECTION OF THE MERITA AREA, VOLTA GRANDE REGION, LAVRAS DO SUL, RS

Evandro Fernandes de Lima (1985)

Adviser: Lauro Valentin Stoll Nardi

Abstract

The Volta Grande region is constituted by a Precambrian to Cambrian volcano­sedimentary sequence which belongs to the Hilário Formation. Au, Cu-, Pb-, and Zn­sulphide mineralizations are found in lodes and brecciated zones which cut across these lithologies. The present paper is concerned with the petrological and geochemical characterization of volcanic and tuffaceous rocks from this region as well as the study of hydrothermally altered rocks for lithogeochemical exploration purposes. Major and trace element geochemistry demonstrates that unaltered rocks have remarkably high contents of alkalis, Ba, Sr, and Rb as well as relatively low contents of Zr, Nb, and Ti. Their geochemical features permit to include the studied rocks in the shoshonitic series. Propylitization is the main hydrothermal alteration, and it is responsible for the sul-phide mineralization and neoformation of chlorite, epidote, and calcite. Such alteration causes chemical changes in original rocks, as indicated by their lower CaO, MgO, and LOI values, and higher Pb contents. The lithogeochemical exploration works carried out in the Merita area (eastern portion of Volta Grande region) were based on the study of Ni, Co, Cu, Pb, Zn, and Ag distribution patterns shown by subsurface samples. Factor analysis and correlations obtained from these elements indicate that the Ni and Co values are related to different lithological types present in this area, while Cu, Pb, and Zn contents have been affected by hydrothermal processes. The independent character of Cu, Pb, and Zn dispersion haloes shows that more than one indicator element must be used for lithogeochemical exploration in this area.

ESTUDO PETROGRÁFICO, PETROLÓGICO E GEOQUÍMICO DA JAZIDA DE MORRO AGUDO, PARACATU, MG

PETROGRAPHICAL, PETROLOGICAL AND GEOCHEMICAL STUDY OF THE MORRO AGUDO DEPOSIT, PARACATU, MG

Renato Antônio Chdiay Dresch (1985)

Adviser: Milton Luiz Laquintinie Formoso

Abstract

The Morro Agudo mineralized area is situated in the Paracatu region, WNW of Minas Gerais State, near the western edge of the São Francisco craton. The Proterozoic lithologies in the Morro Agudo deposit belong to the Vazante Formation, base of the Bambuí Group. The Vazante Formation can be divided into seven facies, which are, in ascending order: Serra do Garrote, Morro do Calcário, Serra do Velosinho Inferior, Serra do Velosinho Superior, Serra da Lapa, Serra do Landim and Morro Agudo. These facies are petrographic units representing different paleo-environments whose characteristics were developed by sea level fluctuations and distribution of stromatolitic reef in a shallow sea.

The Morro do Calcário facies, eminently carbonated, comprises Pre­reef, Reef and Post­reef subfacies. The Pre­reef subfacies is a laminated boundstone composed of SS, SH and LLH­SH type stromatolites. The Reef subfacies is dominantly a combination of boundstone and mudstone. This laminated boundstone is composed of LLH type stromatolites. The Post­reef subfacies is a grainstone composed of intraclasts, oolites and oncolites. Typically, there are three intraformational breccia bodies, each with characteristic features. Geochemical interpretations indicate that grainstone and intraformational breccia with similar matrix, hosts of the ore, are calcitic dolomites. Yet, the mudstone and boundstone were identified as dolomites.

The Conophyton type stromatolites of the boundstones of the Morro do Calcário facies are preserved structures of bluegreen algae or Cyanophyta. Within the cyanophytic algae, species of the orders Chroococcales and Nostacales were important in stromatolite formation. The evidences suggest that nostacalean algae are represented by families Oscillatoriaceae and Scytonemataceae.

A tempoeral sequence of carbonate diagenesis of the Morro do Calcário facies includes neomorphism, cementation, dolomitization, silicification and dedolomitization.

The Morro Agudo mineralization is stratigraphically and structurally controlled. Stratigraphically, the ore occurs in the grainstone and intraformational breccia of the Post­reef subfacies of the Morro do Calcário facies. These rocks are localized along the western flank of the Calcário Hill, considered a stromatolitic bioherm. Structurally, the ore presents its eastern edge limited by a fault approximately N­S. Three prominent fault systems in the Morro Agudo deposit are responsible for the displacement and remobilization of the ore.

Dominant ore minerals are sphalerite and galena. Pyrite, a relatively minor constituent, occurs in bedded bodies composed almost exclusively of pyrite. Three broad categories of ore are delineated: 1. bedded and disseminated, 2. breached, and 3. stockwork. Bedded ore is characterized by its geopetal structure. Breached ore lies within a collapse breccia showing the pull­apart structures in the edges. Stockwork ore occurs in a complex system of faults and fractures.

Morro Agudo ore exhibits a paragenetic sequence of mineral deposition. Early disseminated mineralization was followed by sulfides characterized by colloform texture. These were succeeded by the deposition of sulfides, dolomite, quartz and barite in fractures and vugs. The succession is characterized by overlap and recurrence of the pyrite followed by sphalerite and, after, galena. The rare occurrence of cerussite and goethita in the ore reveals an inexpressive oxidation of the ore minerals.

Within the mineralized sequence, there are several laterally discontinuous layers of fragmented chert. Commonly, the chert fragments show rimmed by pyrite.

The major elements of the Morro Agudo ore include: Zn, Pb and Fe. Mn and Cd are less abundant. Cu is low, however being slightly more concentrated in sphalerite than in galena and pyrite. Within the minor and trace elements present in the principal minerals, the following are mainly noticeable: Ge in sphalerite; Ag in galena; Ga, In, Ni, Co, V and Mo in pyrite. The average of the rates Co/Ni in the pyrite is 0.7.

A diagenetic model is established for the genesis of the ore. Several arguments are used to support the hypothesis that precipitation of the sulfides occurred during the dolomitization and cementation of the host rocks. Among these arguments, are to be emphasized: the high structural competency, textural accessibility and chemical reactivity of the grainstone and intraformational breccia of the Morro do Calcário facies. The ore was formed by the mixing of metal­bearing brines with H2S - rich waters in carbonate rocks. The brines were dolomitizing fluids produced by evaporation, whereas H2S was supplied by bacterial reduction of sulfate.

ORGANO­PETROGRAFIA E ORGANO­GEOQUÍMICA DOS CARVÕES DA JAZIDA DO FAXINAL, MUNICÍPIO DE ARROIO DOS RATOS, RIO GRANDE DO SUL, BRASIL

ORGANIC PETROGRAPHY AND GEOCHEMISTRY OF THE COALS FROM FAXINAL COAL FIELD, ARROIO DOS RATOS MUNICIPALITY, RIO GRANDE DO SUL, BRAZIL

Gilberto Inácio Henz (1986)

Adviser: Milton Luiz Laquintinie Formoso

Associated Adviser: Zuleika Carreta Corrêa da Silva

Abstract

Organo­petrographic and geochemical data of the coal seams from Faxinal Coalfield, Arroio dos Ratos, RS, are presented.

The sequence belongs to the Rio Bonito Formation, Guatá Group, Tubarão Supergroup (Lower Permian of the Paraná Basin) and presents five coal seams from 19.8 cm to 221.4 cm thick. The petrographic analysis comprises organic matter observations in both reflected and transmitted light. Based on reflected light analyses the maceral groups were divided, according to the "Handbook of Coal Petrology". The vitrinite group was divided into "vitrinite A", "B" and "C", according to its petrographic characteristics.

Petrological data show that the coals present high vitrinite/mineral matter ratio and a predominance of mono and bimaceralic microlithotypes (vitrine, vitrinertite and inertite) over trimacerite.

Proximate analysis, including moisture, ash, and volatile matter determinations had its results modified by the high content of minerals. Carbonates, pyrite, and clay minerals produce an increase of the volatile matter content owing to high temperature dissociations, and of the moisture value caused by the lost of water from the clay minerals.

The organic­geochemical study comprises organic determination, pyrolysis, extractable organic matter, liquid and gas chromatographic separation, stable carbon isotopes, and biomarkers.

The organic carbon value ranges from 22.85 to 49.82% and the vitrain concentrate from 65.58 to 72.61%.

Pyrolysis data show that the samples collected at the mine present higher value of S1, S2, and hydrogen index.

The extractable organic matter varies from 1,970 to 5,793 ppm, for the ordinary samples and from 6,800 to 9,750 ppm for the vitrain concentrate.

The extractable organic matter, which was analysed by liquid chromatographic separation, is composed mainly of resines plus asfaltenes, aromatic hydrocarbons, and, less frequently, saturated hydrocarbons (paraffins).

Gas chromatographic separation data show that saturated hydrocarbons present 29 numbers of carbon atoms and high pristane/phytane ratio.

The chromatograms are bimodal, indicating that the paraffins are originated from both aquatic (algae + bacteria) and terrestrial plant material.

The stable carbon isotopes value, from the extractable organic matter, ranges from -24.2 to -26.2%0.

Biological markers parameters (biomarkers) range from 0.47 to 1.21 for the esteranes (C27/29) and, for the terpanes, varie from 0.35 to 0.84 (C24(TS)/C30Hop), from 0.88 to 1.14 (C31(S/R)) and from 0.67 to 1.00 (C32(S/R)).

Petrographic and geochemical data demonstrate that the organic matter is predominantly of woody plant origin, deposited in a limnic (open moor) to limno­telmatic (forest moor) environment.

The rank allows the coal to be classified as "Gasflammkohle" or High Volatile Bituminous A/B, according to DIN and ASTM classification, respectively. However, geochemical, petrographic and technological characteristics indicate a rank equivalent to "Glanzkohle" (Sub­bituminous A).

The coals could be beneficiated by gravimetric methods, since their high ash content is due to pelites intercalation and pyrite.

Low contents of sulphur could also be reached by gravimetric separation of the pyrite.

GEOLOGIA ESTRUTURAL, ESTRATIGRAFIA E PETROLOGIA DE UMA PARTE DO "GREENSTONE­BELT" CERRITO DO OURO, MUNICÍPIO DE SÃO SEPÉ, RS

STRUCTURAL GEOLOGY, STRATIGRAPHY AND PETROLOGY OF A PART OF THE CERRITO DO OURO "GREENSTONE BELT", SÃO SEPÉ MUNICIPALITY, RS

Paulo Ricardo Zarpelon (1986)

Adviser: Hardy Jost

Abstract

The Bossoroca Mine region, São Sepé municipality, State of Rio Grande do Sul, is apparently made up of a fraction of a greenstone­belt fragment.

Structural, stratigraphic, petrographic and geochemical studies have revealed the existence of two large and distinct units, probably of Archean age, Vila Nova Complex and Bossoroca Volcano­Sedimentary Complex (Cerrito do Ouro Greeenstone­Belt).

The Vila Nova Complex is formed by Quartz­Feldspathic Gneiss and by two suites, Gabro­Tonalite­Trondjhe-mite and Granitoid. These units are partially milonitized due to transcurrent faults associated with the first deformation phases of Bossoroca Complex.

The Bossoroca Complex is constituted by the Arroio Lajeadinho and Campestre Sequences. The first one is formed of serpentinites, different magnesian schists, some of them being komatiitic volcanoclastic rocks, and basic schists (rhythmic tuffs, basalts and volcanoclastic toleitic rocks). These rock units exhibit, apparently, a cyclic succession and indicate a volcanic submarine environment. Lenses and layers of cherts and iron formations (oxide and sulfide facies) occur intercalated in these units, and correspond to quiescency periods of the volcanic activity. The Campestre sequence is formed, predominantly, by andesitic, dacitic, riodacitic and riolitic metavolcanoclastic rocks, with calco­alkaline composition. They are, apparently, transitional to the preceding toleitic magmas. Intercalated with these volcanic rocks occur deposits of chemical (cherts and iron formations) and clastic (metassiltites and metarenites in rhythmic succession) origin; the latter is formed by the destruction of volcanic deposits, mainly the felsic ones. In both sequences, volcanic structures and textures are preserved in some places.

The volcano­sedimentary pile was submitted to successive phases of deformation. The first two (D1 and D2) showed isocline folds that are probably associated with thrust faults. In these phases, general metamorphic recristalizations occurred under conditions of greenschist facies at high geothermical gradient (>50°C/km). The third deformation (D3) reoriented the supracrustal units toward the current NE position and, by means of transcurrent and/or thrusting reactivated faults, put the Arroio Lajeadinho and Campestre sequences in contact. In some lithologies, granodioritic intrusions, synkinematic to D3, gave rise to contact metamorphism of hornblende­hornfelsic facies. It is suggested that this deformation is related to efforts originated during the Brasiliano Cycle in the State. D4 and D5 deformations are discreet and related to crustal up­lifts, D4 being followed by granitic intrusions from Brasiliano Cycle that originated domelike arcs in the greenstone. In spite of the intensive tectonic activity, it is still possible to recognize the stratigraphic arrangement, which is oriented in a NE­SW direction.

Previous models considered the Bossoroca Complex as being an ophiolitic sequence. Nevertheless, petrological, petrochemical and stratigraphic characteristics allow to compare this Complex to greenstone­belt structures.

GEOLOGIA, GEOQUÍMICA E PETROLOGIA DO COMPLEXO GRANÍTICO RAMADA E DO GRANITO CERRO DA CRIA

GEOLOGY, GEOCHEMISTRY AND PETROLOGY OF THE GRANITIC RAMADA COMPLEX AND OF THE CERRO DA CRIA GRANITE

Roberto Harb Naime (1987)

Adviser: Lauro Valetim Stoll Nardi

Abstract

The Ramada Granite Complex and Cerro da Cria Granite, situated in the western portion of Sul­Rio-grandense Shield, are intrusive in the lithologies of Cambaí Complex, Vacacaí and Maricá Formations, and are associated with extensive volcanic activity, presently represented by the Acampamento Velho Formation.

The Ramada Granite Complex includes monzogranites, sienogranites and chilled portions, with transitional types. Field evidences suggest they are intimately associated to volcanic rocks occurring in the southern part of this area.

Radiometric data determined an age of 463.5 ± 12Ma for Ramada Granite Complex rocks, and an initial ratio close to 0.710.

The Cerro da Cria Granite occurs as a small and elongate pluton, intrusive in rocks belonging to the Vacacaí Formation, and crosscut by a proeminent fault that displaces the southeastern portion of the pluton. These rocks are hypersolvus granites aging 563.7 ± 4.3Ma.

Geochemically they are high SiO2 granites, alkaline, metaluminous, and probably differentiated by thermo-gravitational diffusive mechanisms as-sociated with fractional crystallization and emplaced in high crustal levels. They have been produced by magmatic activity related to cratonic margin reactivation at the final stage of the Brasiliano Cycle.

ALTERAÇÃO SUPERGÊNICA DE ROCHAS ALCALINAS NA REGIÃO DE LAGES, SANTA CATARINA - FORMAÇÃO DE BAUXITA

SUPERGENIC ALTERATION OF ALKALINE ROCKS IN THE REGION OF LAGES, SANTA CATARINA - BAUXITE FORMATION

Norberto Dani (1988)

Adviser: Milton Luiz Laquintinie Formoso

Associated Adviser: Egydio Menegotto

Abstract

The purpose of this dissertation is to study the bauxite deposits located in the Lages region, Santa Catarina State. An unique characteristic of these deposits is their geographical position, in the southern portion of Brazil, under climatic conditions unfavorable to the lateritization process.

The Lages Dome or Alkaline District of Lages represents an important structure in the context of the Brazilian Geology; the city of Lages is situated in the Southwestern portion of that structure.

The weathering material was studied from the point of view of mineralogy, petrography and geochemistry, complemented by the geomorphology of the landscape - important aspects for the description and characterization of the weathering.

The Alkaline District of Lages has a surface of 2,000 square kilometers and includes rocks of the Paraná Basin sequence as well as alkaline rocks. Among the alkaline rocks, phonolite is the most common. It is important to say that alkaline rocks are like protores of bauxite generation, although in Lages economically significant deposits of this material are concentrated in a restricted portion - Farinha Seca area. In this, are the typical profiles which have a thickness of 10 meters and can be divided in horizons: a rock/weathered rock level in the base of the profile, overlain by a lower clay horizon, bauxite horizon, an upper clay horizon, and the recent organic soil on the top. Microscopy and microprobe data showed that, among the studied minerals, nepheline dissolves completely with weathering leading to the increase of porosity. The orthoclase weathers slower than nepheline and originates an amorphous plasma of silico­aluminous composition, that subsequently can evolve directly to gibbsite or to 10 A halloysite. The pyroxenes concentrate the iron in the rocks, and generate aluminous goethites and secondary gibbsite by weathering processes.

General aspects show that lateritization is not an isolated phenomenon in the area; it is, conversely, spread and associated with different rocks, such as diabase in the Lages region, or correlated with the weathering profile developed in the basalt rocks of Vacaria region, Rio Grande do Sul Stat Thus, problably not only the rock susceptibility was the responsible mechanism for the bauxite formation, but also geomorphological factors were important to preserve this accumulation of succeeding erosive events.

CONTEXTO GEOLÓGICO E GEOQUÍMICA DAS LAVAS MÁFICAS DA SEQÜÊNCIA VULCANO­SEDIMENTAR QUATRO MENINAS, MUNICÍPIO DE INDIAVAÍ, MT

GEOLOGIC SETTING AND GEOCHEMISTRY OF THE MAFIC LAVAS OF THE VOLCANO­SEDIMENTARY QUATRO MENINAS SEQUENCE, INDIAVAÍ MUNICIPALITY, MT

Jayme Alfredo Dexheimer Leite (1989)

Adviser: Hardy Jost

Abstract

The geology of the southwestern portion of Mato Grosso State is constituted by rock associations that characterize an evolution similar to the one found in granite greenstone terrains. The Quatro Meninas Volcano Sedimentary Sequence is a good example of these rock associations. This Sequence has three units, from bottom to top: a Mafic Volcanic Unit, a Chemical Unit, and the Felsic Volcanic Unit. The Mafic Volcanic Unit is the most important and occurs in 85% of the studied area.

The petrographic data identify one metamorphic event of greenxistesfacies conditions. The geochemical characteristics presented by the Mafic Volcanic Unit lead to the division of these lavas into two groups: one, characterized by komatiitic affinity and represented by komatiitic basalts; the other is characterized by tholeiitic affinity and represented by normal tholeiites and iron rich tholeiites. The magma generation of these two groups was of the same source, by means of different episodes of partial melting of different amount. These lavas spread only under subaqueous conditions.

LEVANTAMENTO GEOQUÍMICO ORIENTATIVO PARA FLUORITA NO ESTADO DE SANTA CATARINA

ORIENTATIVE GEOCHEMICAL SURVEY FOR FLUORITE IN SANTA CATARINA STATE

Carlos Alberto Kirchner (1990)

Adviser: Lauro Valentim Stoll Nardi

Associated Adviser: Marcelo José Ribeiro

Abstract

This dissertation deals with the information obtained from the "Stage 3 ­ Methodology research" (Etapa 3 - Pesquisa de Métodos) of the "Fluorita no Sudoeste de Santa Catarina" project.

Geological reconnaissance work confirmed the presence of Proterozoic granitic lithologies hosting fluoritic mineralization (Pedras Grandes and Guabiruba intrusive suites) described in earlier papers. The sedimentary sequence of the Itararé Group and basic rocks of que Serra Geral Formation are also found together with less common acidic rock dikes and siliceous veins. Fluoritic lodes have variable dimensions showing up as lenses thinning laterally or in depth.

There were collected 234 samples from fluvial water, 236 from streamsediments, 17 from pan concentrates and 336 from soil. The results pointed out to fluvial water as the most representative sampling element concerning to regional or semi­regional prospection, owing to the good fluorine detection, the sampling quickness, its low cost and the analytic facility. Stream sediments are considered as a second option for fluorite regional prospective programs. For detailed prospective programs, granitic soil studies show that fluorine can be considered as a direct indicator for the presence of fluoritic mineralization.

The dispersion spacing from lodes, even to fluvial water or soils, shows similarities with orientative researches carried out in other places with similar characteristics.

GEOQUÍMICA E GEOLOGIA ESTRUTURAL DA MINA DE OURO DE ZAPUCAY - DEPARTAMENTO DE RIVERA, REPÚBLICA ORIENTAL DO URUGUAY

GEOCHEMISTRY AND STRUCTURAL GEOLOGY OF THE ZAPUCAY GOLD MINE - RIVERA DEPARTMENT - URUGUAY

Rogério Noal Monteiro (1990)

Adviser: Léo A. Hartmann

Abstract

The Zapucay gold deposit, located in Rivera, Uruguay, is internally located in relation to a ductile shear zone, which later evolved into a ductile­fragile zone. It was studied from the geochemical and structural points of view, unified for an overall understanding of the processes of hydrothermalism and mineralization. Detailed mapping of the mine was performed, including the structural parameters, followed by multivariate statistical studies of a matrix of geochemical data, including major, trace and rare earth elements for 66 samples of rock and ore. Most of the samples were obtained from the mine, but some were taken from the region around. Thus, the pre­shearing lithologies were characterized, and in the mine also the alteration. The host lithologies to the mineralizations are shoshonitic in compositions corresponding mostly to porfiritic quartz­monzonites now turned into augen­gnaisses mylonites. TheBengoechea Granite has composition close to SiO2 = 62.20%; TiO2 = 0.76%; Al2O3 = 15.10%; Fe2O3 = 1.60%; FeO = 2.78%; MnO = 0.04%; MgO = 2.15%; CaO = 3.32%; Na2O = 4.31%; K2O = 3.21%; P2O5 = 0.33%; Ba = 1,644ppm; Sr = 944ppm; Zr = 297ppm; Nb = 34ppm; Rb = 65ppm. The REE have distributions [(Ce/Yb)N = 15.0; Eu/Eu* = 0,85; õETR ~ 120] close to syntexis granites.

The syn­shearing hydrothermal alteration occurred during amphiblite­ ­facies conditions. Alteration was most pronounced where shearing was most intense. The ore zone was affected by sericitizations, silicification, carbonization and albitizations. The Pb, CO2, Fe2O3 and the Eu/Eu* > 1 dispersion halos were coincident or somewhat larger tham the mineralization.

The Zapucay gold deposit may be classified as a shear­related, vein­type fold deposit.

GEOLOGIA, PETROLOGIA E GEOQUÍMICA DAS ROCHAS OCORRENTES AO LONGO DO RIO AGUAPEÍ, SUDOESTE DO CRATON AMAZÔNICO - PONTES E LACERDA - MT

GEOLOGY, PETROLOGY AND GEOCHEMISTRY OF THE ROCKS OCCURRING ALONG THE AGUAPEÍ RIVER, IN THE SOUTH WEST OF THE AMAZON CRATON - PONTES E LACERDA - MT

Márcia Aparecida de Sant'Ana Barros Pinho (1990)

Adviser: Léo Afraneo Hartmann

Abstract

The present dissertation characterizes the chemistry and petrography of the rocks along the Aguapeí River, giving emphasis to the granitoids and amphibolites.

Thirteen granitoids of predominant calc­alkaline composition were examined in dispersion diagram for major oxides and trace elements. Differentiation Index versus major oxides indicated concordance to the igneous rocks.

The contents of REE are impoverished, with unfractionated patterns, similar to the granitoids of mantelic origin showed by granitoids of the South China. Discussion was developed in relation to the composition of the source of these rocks.

The amphibolites occur as xenolits in tonality rocks, as tectonics banded either as dikes in gneissic rocks. In thin sections they exhibit remaining igneous textures in some samples and tectonic and metamorphic textures in others.

Fourteen samples showed a compositional gap marked by TiO2 and Ni. These rocks have characteristics of Tholeiites Basalts. REE patterns are similar to those of Archean basalts TH2. The study above indicates that these bodies are orthoamphibolites.

Tonalites may carry significant amounts of garnet.

Some mafic xenolits granulites were observed in the field.

ESTUDO DAS ROCHAS ENCAIXANTES E VEIOS MINERALIZADOS A OURO DO GRUPO CUIABÁ, NA REGIÃO DENOMINADA "GARIMPO DOS ARAÉS", NOVA XAVANTINA - ESTADO DO MATO GROSSO

STUDY OF THE GOLD­BEARING VEINS AND THEIR HOST ROCKS, CUIABÁ GROUP, IN THE "GARIMPO DOS ARAÉS" REGION, NOVA XAVANTINA - MATO GROSSO STATE

Francisco Egídio Cavalcante Pinho (1990)

Adviser: Léo Afraneo Hartmann

Abstract

The present dissertation made use of geochemical and petrographic studies to characterize the Nova Xavantina Gold Deposit and host rocks.

Through major and trace elements analysis, the rocks were characterized as a volcanic­sedimentary sequence.

REE patterns of the metavolcanic rocks appear similar to those of tholeiitic basalts.

Banded iron formations exhibit positive Eu prominent anomalies, common to the Proterozoic bifs.

Compositional variation profiles of vein­host rock established the paragenesis: SiO2, Fe2O3, P2O5, Cu,Pb, Zn, As, Cd, Ag, Sb, Se, Hg and Au for the auriferous vein, which is represented by opaque minerals: galena, pyrite, chalcopyrite and gold.

The evaluation of the petrologic and geochemical data suggests that the local rocks were deposited in a subaqueous environment with simultaneous volcanism and sedimentation, problably of the back­arc model.

This gold had its source in existing disseminations in a volcano­sedimentary sequence, which was transported by hydrothermal fluids of metamorphic origin, rich in sulphides, and deposited in quartz vein in graphite layer when the environment became reducting.

ALTERAÇÃO HIDROTERMAL DAS ROCHAS BASÁLTICAS ASSOCIADAS ÀS AMETISTAS

HYDROTHERMAL ALTERATION OF THE BASALTIC ROCKS ASSOCIATED WITH AMETHYSTS

Rejane Maria Scopel (1990)

Adviser: Milton Luiz Laquintinie Formoso

Associated Adviser: Alain Meunier

Abstract

The more common products of hydrothermal alteration in the geode and veinlet­bearing basalts in São Gabriel-Planalto are the clay minerals.

In geode­bearing basalt, the groundmass comprises almost fresh plagioclase and augite crystals, olivine entirely altered to saponite and celadonite, opaque crystal laths and glass replaced by Fe saponite, celadonite and saponite/chlorite mixed­layer. Phenocrysts of plagioclase are locally altered to saponite and clinopyroxenes (augite and pigeonite) are altered only in fractures.

Two alteration bands fill the geode (from the rock to the internal part): the first one is constituted of Fe saponite and ferril­montmorilonite cryptocrystalline beige and brown, orange saponite and dark green matrix constituted of saponite, saponite/chlorite mixed­layer and mixture of saponite+celadonite. The second band is made up of silica (mainly chalcedony), smectite and mordenite.

The rare visicles are filled from the external to internal parts by: orange Fe saponite, misture saponite + celadonite and fibrous greenish yellow to green celadonite.

The veinlet­bearing basalt shows the same primary components as the geode­bearing basalt.

The glass is a little anysotropically close to the veinlet but is progressively altered to a beige matrix and black material, as the distance increases farther from the veinlet. The microphenocrysts of olivine are totally replaced by beige to reddish saponite (in the borders and intramineral fractures) and green celadonite (rare in the central zone).

The plagioclases and augite of the groundmass are not much altered and the phenocrysts are locally altered to brown and greenish brown matrix (plagioclase and augite respectively).

The vesicles are filled parcial or totally by brown ferril­montmorillonite (external part) and fibrous­radiate saponite/chlorite mixed­layer (internal part), or just by a brown ferri­ ­montmorillonite.

The veinlet is filled (from the periphery to the center):

- brown clay mineral (ferri­ -montmorillonite),- prismatic zeolite (heulandite) and/or fibrous­radiate saponite/chlo-rite mixed­layer and/or fibrous mordenite and/or calcite, and- fibrous­radiate saponite/ chlorite mixed­layer.

CARACTERIZAÇÃO GEOLÓGICA E GEOQUÍMICA DAS SEQÜÊNCIAS ULTRAMÁFICA E VULCANO­SEDIMENTARES DA REGIÃO DE BOSSOROCA - RS

GEOLOGICAL AND GEOCHEMICAL CHARACTERIZATION OF THE ULTRAMAFIC AND VOLCANO­SEDIMENTARY SEQUENCES OF THE BOSSOROCA REGION - RS

Wilson Wildner (1990)

Adviser: Leo A. Hartmann

Abstract

The semi­detailed geologic mapping (1:25,000) of the Bossoroca Region produced several data of major, minor and trace elements, REE and PGE. They were worked out and lead to the characterization of a part of the mafic­ultramafic Arroio Lajeadinho and the meta­volcano­sedimentary Campestre Sequences, in the Porongos Group.

The detailed work in the Campestre Sequence led to the description and characterization of the diagnostic rocks of the processes associated to volcanogenic events. Their principal facies are:

_ Flow Generated Deposits:

- Pumice and ash flow

- Lava flow

_ Base Surge Generated Deposits

_ Air­Fall Generated Deposits

- Dust and Ash Clouds

_ Epiclastic Deposits:

- Sediments Under Water Level

- High­Density Flow (Lahaar Type)

These deposits suggest that the volcanogenic avent was a high explosive one and generated a deposition comparable to an extract volcano, possibly associated to a Plianian eruption process.

This volcanogenic association is lithochemically composed of trachy-andesites, andesites and dacites which are calc­alkaline, hypersthenic, with sodic alkalinity and moderate amount of alumina.

The lithochemical treatment showed that these rocks derived from just one volcano­magmatic event whose compositional variations represent the fractionations and modifications that took place during the evolution of the magmatic process.

The Arroio Lajeadinho Sequence has three fundamental lithologic associations: a) gabbroic and basaltic rocks; b) serpentinitic roks; and c) metasomatic rocks.

The data of the portion with gabbroic and basaltic bodies point to normal tholeiitic rocks with low potassium, associated with an arc regime.

The serpentinic rock association is composed by variable portions of cumulatic protoliths that seem to come from olivinic liquids such as harzburgitic, lherzolitic and dunitic ones, related to Alpine Complexes.

The interpretation from the obtained data is that the ultramafic rocks are allochthonous bodies, put in place together with a volcanic arc sequence, associated to volcanoclastic and sedimentary rocks, during a process of crustal shortening and closing of a marginal basin that is composed, at least in part of it, by an oceanic floor and placed near a magmatic arc.

GEOQUÍMICA DOS CARBONATOS RESERVATÓRIOS DA FORMAÇÃO MACAÉ, DOS CAMPOS DE PAMPO E ENCHOVA, BACIA DE CAMPOS, BRASIL

GEOCHEMISTRY OF THE CARBONATE RESERVOIRS OF THE MACAÉ FORMATION, IN THE PAMPO AND ENCHOVA FIELDS, CAMPOS BASIN, BRAZIL

Luís Eduardo de Souza Robaina (1990)

Adviser: Milton Luiz Laquintinie Formoso

Abstract

The aim of this dissertation is the analysis of reservoir rocks of Pampo and Enchova fields, Macaé Formation, RJ, Brazil.

The Macaé Formation, subject of this research, represents the episode of Open Continental Margin, narrow sea stage, of tecto­sedimentary shelf evolution. The marine conditions are established at the beginning of Albian, owing to the spreading of the proto­oceanic gulf. During the evolution of the proto­oceanic gulf to narrow seas, a relative tectonic stability and a clear marine water circulation over the Continental shelf were very good conditions for the development of a carbonatic shelf. These Albian carbonates consolidated the marine sedimentation and represent the transition of a hyper­restricted system to an oceanic one.

Those carbonatic rocks also constitute a deposition on shoal, in the shallow, hot and restrict marine water environment. This is well demonstrated through paleontological and geochemical data. The chemical values of minor and trace elements in the whole rock analyses are similar to the sediments originated in shallow marine shelfs. The oxygen and carbon isotopic values are also characteristic of sediments deposited in shallow and hot marine waters. Through analyses of Ù010 of samples less affected by diagenesis, temperatures close to 26°C can be inferred for the water in the depositional environment. This restricted environment with high salinity is evidenced by the not varied species of foraminifera and high alkaline and chlorine values in the whole rock analyses. The content of ÙC13 close to +4 is in agreement with this idea.

The redox conditions were analysed through the geochemical behaviour of Ce. In relation to La and Nd, the content of Ce slightly depleted to non­depleted characterizes different redox conditions from present day. This is interpreted as the characteristics of a Macaé restrict sea with few oceanic circulation.

The distribution of LREE in relation to HREE may represent a low homogeneous continental contribution. In this way, a weak continental weathering and low organic matter deposition are suggested. These ideas agree with paleontological data (Dias­Brito, 1982) and contents of Fe, Mn and insoluble residue.

The carbonates of Macaé Formation were deposited in marine environment, just after starting their diagenetic history. In the marine environment the alochemical grains underwent an intense micritization caused, probably, by algae. The cementation occurs as a fibrous fringe around the grains. Microprobe data show a significant content of magnesium and undetectable quantity of strontium, suggesting high magnesium calcite as an important factor for this cementation.

The subaerial exposure led to a dissolution of grains and cement.

The passage through a freh water phreatic environment is marked by a complete mineralogical transformation, in which aragonite, magnesium calcite of the formed sediments have been changed to rocks constituted only of low magnesium calcite. The trace and isotopic data denoted that the mineralogical stabilization process occurred in a relatively "closed" system, although the "closing degree" is dependent of local conditions. In this environment, neomorphism, syntaxial cementation in the echinoids and probable rhombohedrical fringe around the grains occur. The rhombic habit of the fringe crystals suggests they are originated in a low salinity environment. The cementation as spatic mosaic is well developed in the Enchova field and less advanced in the Pampo field. The continuous cementation in fresh water phreatic zone can occur because of the rhombohedrical fringe has been transformed into a mosaic that fulfilled the pores. Chemically, the change of a rhombohedrical fringe to a mosaic, due to a longer time of diagenetic fluid residence, can be indicated by the similar value to the trace elements of fringe and mosaic. According to Franz (1987), the great cementation difference between Enchova and Pampo field may not undicate similar relief conditions, because structurally higher areas could be more favorable for the development of fresh water lenses. The low positive values of ÙC13 and the negative values of ÙC10, besides the lower Sr content of Enchova's samples, led to this interpretation.

During the mesodiagenesis, the chemical compactation, dissolution and fracture cementation are important processes.

The dolomitization should be associated with saline solution. High magnesium calcite can be an important source of magnesiun.

ESTUDO PETROGRÁFICO E GEOQUÍMICO DE CARVÕES DA JAZIDA DE SANTA TEREZINHA, RIO GRANDE DO SUL, BRASIL

PETROGRAPHICAL AND GEOCHEMICAL STUDY OF THE COALS FROM SANTA TEREZINHA COALFIELD, RIO GRANDE DO SUL, BRAZIL

Carla Viviane Araújo (1990)

Adviser: Zuleika Carreta Corrêa da Silva

Abstract

The results of organo­petro-graphic and geochemical studies of the coal seams from Santa Terezinha Coalfield, NE of Rio Grande do Sul State, Brazil, are presented.

Several coal seams and thin coal layers obtained from cores of the boreholes 2TG­96­RS, 2TG­227­RS and 2TG­230­RS were studied. These seams were named ST1, ST2, ST3, ST4, ST5, ST6.1 and ST6.2 by the Companhia de Pesquisa de Recursos Minerais (CPRM).

The sequence belongs to the Rio Bonito Formation, Guatá Group, Tubarão Supergroup (Permian of the Paraná Basin).

The petrographic studies comprised combined analysis (maceral and micolithotypes) and vitrinite reflectance measurements according to the Handbook of Coal Petrology.

The coals are rich in mineral matter, mainly clay. The most frequent maceral groups are vitrinite and inertinite. Among the microlithotypes the most abundant are carbargilite, rock and vitrite.

The coal rank ranges from High Volatile Betuminous A to High Volatile Betuminous B (ASTM) based on vitrinite reflectance, volatile matter (d.a.f.) and moisture. Some coal layers are heat affected by intrusive bodies.

Proximate analysis including moisture, volatile matter, ash and fixed carbon determinations indicated high contents of ash in almost all the samples. A statistical study revealed a good correlation between ash and volatile matter.

The microlithotype association indicated that an open­water moor (limnic facies) prevailed during the formation of the coal seams. The occurrence of limno­telmatic facies was very restricted.

The organo­geochemical analysis comprised total organic carbon determination, pyrolises rock­eval, extractable organic matter, liquid and gaseous chromatographic separation, biomarkers and stable carbon isotopes.

Pristane/phytane ratios are always higher than 2 reaching up to 7.4. Pristane/n­C17 and phytane/ n­C18 varies from 0.4 to 6.3 and from 0.11 to 0.87 accordingly.

The terpane analysis showed frequently a predominance of tetracyclic over tricyclic compounds, high relative concentration of low molecular weight hidrocarbon compounds (C19 and C20) among the tricyclic terpanes, and high relative abundance of trisnorhopane (Tm) and norhopane. The investigation of steranes demonstrated a predominance of C29 compounds.

Results obtained by geochemical investigation indicate a great terrestrial derived material input.

The organic facis A, B, C and C* were determined by using integrated data, based on compositional differences which were better controlled by the results from stable carbon isotops and maceral composition.

GEOLOGIA E GEOQUÍMICA DO COMPLEXO CAMBAIZINHO, SÃO GABRIEL - RS

GEOLOGY AND GEOCHEMISTRY OF THE CAMBAIZINHO COMPLEX, SÃO GABRIEL - RS

Marcus Vinícius Dorneles Remus (1990)

Adviser: Léo Afrâneo Hartmann

Abstract

Geologic mapping performed by the author in the Cambaizinho area resulted in the separation of the Cambaizinho Complex. This includes sedimentary and mafic­ultramafic metamorphosed sequences which closely intertongue all over the supracrustal association.

The metasedimentary sequence is built up mainly by quartz­feldspathic gneisses and less abundant banded amphibolites with minor amounts of quartzites. These supposedly represent metamorphosed, rithmically banded, subaqueous arenaceous marly sediments. At some levels of restrict occurrence, representing an iron­rich composition, staurolite­bearing metamorphic assemblages suggest a medium grade metamorphism to this region. Interfingered serpentinites, some varieties of magnesian schists and fine grained amphibolites enclosed in the metasedimentary rocks suggest lava flows and low depth intrusions of basic/ultrabasic composition. These volcanic magmatic rocks altogether with gabro bodies and interlayered chemical sediments built up the mafic­ultramafic sequence.

Cambaizinho Complex represents the northern segment of a supracrustal, multideformed linear belt trending NNE, which stretches from this area to Paso do Ivo in the south.

Four deformation phases were recognized for this area, being the first and the second (D1 and D2) associated to regional metamorphic events, M1 and M2. The oldest metamorphic episode (M1), signaled by diagnostic paragenesis in metapelites, reached the amphibolite facies (staurolite zone) being represented in magnesian rocks by olivine­tremolite± talc (meta­serpentinites) and horn-blende­oligoclase/andesine in meta-basites. The M2 metamorphic event, younger, is represented by greenschist facies whose mineralogic assemblages are associated with S2 foliation irregularly distributed along the belt. Physical conditions for M1 metamorphism of intermediate values for P/T are comparable to those of the Dalradian metamorphism.

Granitic intrusions with the form of sheaf­like bodies, belonging to the second phase of deformation (D2), give the minimum Rb/Sr age of 661 ±29 Ma for the whole complex and were named Sanga do Jobim Granitoids.

The whole compositional range of the mafic­ultramafic sequence, separated by means of petrographic criteria and major elements contents, are named serpentinites and olivine­ ­talc ultramaphites (komatiitic cumulates), magnesian talc schists and chlorite­ ­amphibole schists (komatiites),chlorite­hornblende schists (basaltic komatiites) and amphibolites and meta­gabros (tho-leitic basalts and gabros).

The lithologic types above are thought to have originated by different degrees of partial mantle fusion, as suggested by MgO hiatus (11­17%) and various ETR patterns found for amphibolites and meta­gabros (tho-leites) and serpentinites/magnesian schists (komatiites). Compositional variations in each group were controled by fractionation (accumulat-ion/extraction) of olivine and minor orthopyroxene (serpentinites and olivine­talc ultramaphites), pyroxenes and lesser amounts of olivine (talcmagnesian schists), clinopyroxenes (chlorite and amphibole schists and chlorite­hornblende schists), clino-pyroxene and plagioclase (amphi-bolites and meta­gabros).

Abundancies and enriched patterns of LREE altogether with low values of Al2O3/TiO2 and CaO/TiO2 rates of magnesian schists of A & B layers suggest derivation of this material from feeble percentages of fusion of the mantle enriched in incompatible elements. Negative Ce and Eu anomalies in most rocks of the mafic­ultramafic sequence point to protolites submited to alteration in submarine environment.

PETROLOGIA DO GRANITO ARROIO MOINHO (CANGUÇU/RS) - GEOQUÍMICA E DEFORMAÇÃO

PETROLOGY OF THE ARROIO MOINHO GRANITE (CANGUÇU/RS) - GEOCHEMISTRY AND DEFORMATION

Marcia Elisa Boscato Gomes (1990)

Adviser: Lauro Valentim Stoll Nardi

Abstract

The Arroio Moinho Granite represents a synkinematic intrusion related to the establishment of the Canguçu Dorsal shear zone, which has a direction of N35­75°E and sinistral sense of movement and cuts the east side of the Sul­riograndense Shield.

It is composed of monzo and sienogranites with chemical affinitties intermediate between calc­alkaline and alkaline series, related to tardi­orogenic rocks intruded in mature magmatic arcs.

The shearing originated mylonitic rocks described as protomylonites, orthomylonites and ultramylonites, by progressive deformation of the origin-al granitic rock.

At microscopic scale it was observed a particular behavior for each mineral: quartz with essentially ductile deformation and feldspars with brittle­ductile behavior. Associatedwith the deformation there were chemical and mineralogical changes including amphibole and oligoclase destruction and neoformation of K­feldspars and biotite followed by formation of new mineral phases as albite, epidote, titanite and white mica. Chemical changes between minerals represent the redistribution of elements, mainly Fe and Ti, with little lose of Ca and gains of Na.

The mylonitic microstructures show that deformation occurred by processes of strain enhanced diffusion, crystal plasticity and fracture, with strain softening mechanisms playing an important role.

These microstructures, associat-ed with chemical and mineralogical changes, indicate temperatures around 350­450°C, corresponding to greenshist facies conditions, for the formation of mylonitic rocks.

ALTERAÇÃO INTEMPÉRICA DE ROCHAS VULCÂNICAS ÁCIDAS NA REGIÃO CENTRAL DO ESTADO DO RIO GRANDE DO SUL - BRASIL

WEATHERING ALTERATION OF THE ACIDIC VOLCANIC ROCKS IN THE CENTRAL REGION OF RIO GRANDE DO SUL STATE - BRAZIL

Nelson Vicente Lovatto Gasparetto (1990)

Adviser: Egydio Menegotto

Abstract

This dissertation presents the study of the weathering of volcanic rocks in the central region of Rio Grande do Sul State. The acidic flood is mainly composed of riolite and secondarily of volcanic glass. The alteration takes place under subtropical climate with defined seasons and mean annual precipitation above 1200 milimeters.

The topography is smooth with gentle slopes with low hills and a hundred of meters declivity. The soil is not well developed in the predominant area, but in the even areas on the top latossoils can be found. The vegetation is characterized by grammineae and ciliary forest.

The alteration occurs over two well characterized forms: 1) concentric weathering, developing levels with alteration through its periphery; 2) vertical profiles, where the alteration happens in the main rock, fluently and continuously producing a variable of soil covering.

Intemperism makes successive destruction of minerals in the following crescent order of stability: carbonate < pyroxene = glass < plagioclase < alkall feldspar < magnetite < quartz.

The pyroxene weathering produces smectite and amorphous materials, as iron helps out the goethite formation. Plagioclase produces smectite with low concentration of kaolinite. Alkall feldspar intergrown with quartz produces kaolinite and traces of illite. Magnetite leads to goethite formation, but the latter can be found together with quartz as a residual fase. The amorphous products (Si, Fe and Al), evolve to crystallization in the form of oxides and hydroxides in small proportion.

Through the isovolumetric method the loss and gain percentages of the chemical elements were established in the different levels of weathering. Therefore, the following sequence of relative mobilities could be found: a) Ca > P > Na > K > Si > Mg > Mn > Al > Fe > Ti > H2O; minor elements Rb > Sr > Ba > Ni > Zn > Li > Pb > Cu > Zr > Co.

The geochemical evolution shows high loss of soluble elements and moderate loss, even of those elements known as stable. Some elements of high mobility in the supergen cycle have shown and increased concentration at the higher levels of alteration, kept by adsorption of clay minerals.

The rare earths minerals are also fractured during the weathering process.

GEOLOGIA E PETROQUÍMICA DOS GRANITÓIDES DA REGIÃO DE MONTE BONITO - PELOTAS - RS

GEOLOGY AND PETROCHEMISTRY OF THE GRANITOIDS OF THE MONTE BONITO REGION - PELOTAS - RS

Ruy Paulo Philipp (1990)

Adviser: Lauro V.S. Nardi

Associated Adviser: Luís A. D'Ávila Fernandes

Abstract

This dissertation studies some granitic rocks of the eastern part of the Sul­Riograndense shield, in Monte Bonito region, Pelotas, RS. These rocks were stratigraphically separated based on their structural geology, intrusion/inclusion relations and petrochemical compositions.

Two plutonic suites were distinguished: Pinheiro Machado Suite and Dom Feliciano Suite.

The rocks of Pinheiro Machado Suite are the main purpose of this work. They were divided into two mapeable units, named Monte Bonito Granite and Equigranular Granodiorites. The Monte Bonito Granite is composed of monzogranites and porphyritic granodiorites characterized by tabular megacrysts of K­feldspars. It is exposed near Monte Bonito as an eastwest elongated body which cuts the equigranular granodiorites. These are dominantly equigranular, median to coarse grained, and show an irregular and discontinuos banding given by mafic schlierens. The contacts between these granits are marked by lobate and gradational limits and by the presence of enclaves of one unit inside the other in this region. They have inclosed xenoliths of high grade metamorphic rocks (ortogneisses and amphibolites), mafic enclaves (microdiorites) and equigranular diorites. The last ones belong to the suite and are considered as its basic terms.

The structural characterization shows the occurrence of two regional events marked by the development of two groups of Ductile Shear Zones, named Subhorizontal Zones and Subvertical Zones. The preliminary study of the tectonic foliations suggests the syntectonic emplacement of the equigranular granodiorites to the Subhorizontal Zones and syn to tardi­tectonic of the Monte Bonito Granite to the same Zone.

The petrochemical study of the major and some trace elements (Rb, Sr, Ba, Zr) shows preliminarly the calc­alkaline nature of the Pinheiro Machado Intrusive Suite.

ESTUDO DAS ALTERAÇÕES DO METANORTOSITO DE CAPIVARITA - RS

STUDY OF THE ALTERATIONS OF THE CAPIVARITA METANORTOSITE - RS

Marcos Antônio Tedesco (1990)

Adviser: Milton Luiz Laquintinie Formoso

Abstract

The purpose of this dissertation is the study of different kinds of alteration that occur in the Pre­ ­Cambrian metanortosites of Capivarita (RS) region, emplaced in the Sul­Riograndense shield, and partially intruded by granitic rocks in its central part.

This study revealed that those rocks had been affected by pre­meteoric activities (hydrothermal alteration), before being exposed to the supergenic system related to the interface lithosphere­atmosphere.

Mineralogical and structural changes demonstrate that the mineralogy of hydrothermal alteration evolved in successive zones either in selective pervasive or fissured forms, related to solutions that percolate from the rock to open spaces.

Sequential and zoned crystalo-chemical paragenesis indicates that the hydrothermal system acted in three successive processes of different intensities:

- Incipient potassification, with the formation of biotite + K­feldspar + albite + quartz;

- Extensive propilitization, that resulted in the neo­formation of epidote + chlorite + carbonate;

- Filitization that was super-imposed on the others, and generated sericite + muscovite + quartz.

These processes were inter­ ­related and syncronous, but not sufficiently strong to promote argilization.

The intrusion of granitic rocks possibly promoted the hydrothermal alteration and was responsible for the upraise of the central part of the area, opening spaces to the percolation of meteorical waters. This contributed to the weathering alterations which resulted in the formation of the extensive deposits of residual kaolinites.

O SISTEMA HIDROTERMAL FÓSSIL DE VOLTA GRANDE - LAVRAS DO SUL- RS

THE FOSSIL HYDROTHERMAL SYSTEM OF VOLTA GRANDE - LAVRAS DO SUL - RS

André Sampaio Mexias (1990)

Adviser: Milton Luiz Laquintinie Formoso

Abstract

The Volta Grande region comprises a sequence of volcanic and pyroclastic rocks (tuffs and breccias) of Pre­Cambrian to Cambrian age, that belongs to Hilário Member of Crespos Formation.

These rocks are intruded by the transitional granite of Lavras Granitic Complex, what produced a contact aureole (0­500m width), with a metamorphic grade which varies from low­amphibolite to greenschists facies.

The granitic intrusion acted as a source of heat in the production and maintenance of a hydrothermal system, where the petrochemical character and the zonation patterns of the alteration products are very similar to those observed in the porphyry copper­type deposits.

After the formation of the hornfelses, near the contact of the granite, the final fluids of the granitic magmatism, flowing through interconnected fractures, infiltrated the country rocks and crystallized the higher temperature mineral parageneses of the hydrothermal system (potassic alteration). By the influence of the conductive heat transfer, occurred the crystallization of epidote + chlorite (+ actinolite near the granite contact), which took place through the stagnant pore and microcracks (propilitic alteration), where the original rock composition influenced the chemical character of the secondary minerals.

In a destructive way, the fluids with high H+ activity, acted in the rock, percolating the fractures after and/or synchronously with the propilitic processes, in temperature conditions equal or slightly superior (300°C), producing illite + chlorite + quartz + pyrite.

Finishing the hydrothermal activity, or being associated to another related system, such as more recent faults, occurred the circulation of high PCO2 and fO2 fluids, through the fractures, what promoted the crystallization of calcite, corrensite, hematite and feldspars.

This fossil hydrothermal system is responsible for the remobilization and concentration of metals, like Au, Cu, Pb and Zn, producing ore deposits.

PETROGRAFIA DOS GRANITÓIDES DEFORMADOS NA ZONA DE CISALHAMENTO DORSAL DE CANGUÇU (PIRATINI/QUITÉRIA, RS)

PETROGRAPHY OF THE DEFORMED GRANITOIDS AT THE CANGUÇU DORSAL SHEAR ZONE (PIRATINI/QUITÉRIA, RS)

Maria José Maluf de Mesquita (1991)

Adviser: Luís Alberto D'Ávila Fernandes

Abstract

The Canguçu Dorsal (CDSZ) is a sinistral transcurrent shear zone of crustal scale, with a NE trend. This zone has affected and controlled the emplacement of granitic rocks of Brazilian age.

The granitic rocks related to the CDSZ may be divided into pre, syn or tardi to pos­tectonic (D2).

The pre D2 metagranitoides, belonging to Canguçu Complex and Arroio dos Ratos Gneissic Complex, have calc­alkaline character and were deformed during the D1 tangencial regime with a E­W translation direction of rocks masses. That is characterized by dextral sense of moviment. Linear D1 structures include stretching and mineral lineations and fold axes with L­W to NW preferential orientation, and low plunge. Microstructural evidence of crystal plasticity, as subgrains and new grains in feldspars, shows thatD1 deformation occurred in metamorphic conditions equivalent to amphibolite facies.

The syn­D2 (CDSZ) metagranitc roks are calc­alkaline to high­K calc­alkaline and peraluminous (Quitéria and Arroio Francisquinho, respectively).

The pre and syn­D2 metagranitic rocks present an early homogenous mylonitic foliation and are cut by several late discrete shear zones (D2), that produce protomylonites, orthomylonites and ultramylonites. The change in feldspat behavior, from ductile to brittle, and the formation of a metamorphic­hydrothermal mineral assemblage composed of albite, epidote, white mica, biotite and/or chlorite demostrate that this tardi­D2 deformation took place under predominantly retrogressive conditions (green schist facies).

ALTERAÇÃO DAS ROCHAS NO MACIÇO ALCALINO DE ANITÁPOLIS - SC

ROCK ALTERATION IN THE ANITÁPOLIS ALKALINE MASSIF - SC

Vitor Paulo Pereira (1991)

Adviser: Milton Luiz Laquintinie Formoso

Associated Adviser: René Flicoteaux

Abstract

The alkaline massif of Anitápolis was dated in 130 millions of years. It has a semicircular area of 6 km², which is the product of many alkaline injections responsible for the fenitization of the granitic wall­rocks and for an autometassomatism where the end product results in rocks of the alkali­syenites, nepheline­syenites, ijolites and phlogopite­piroxenitic series distributed in concentric aureoles, where the most felsic terms are next to the edge of the body.

The hydrotermalism, a generator of an apatitic phosphate reserve with 320 millions of tons, has the principal concentration in the glimmerites and late veins wich followed by at least two carbonatitic generations prevailing the sövitic terms.

The alterite profile developed on those rocks is little evolved, what hinders the existence of higher apatitic phosphate purports in this profile in relation to the inaltered rock.

In the alteration study of different minerals the micromorphologic aspects were analyzed trying to follow the chemical modifications with the evolution of supergenic processes. To do this, analyses were made by X­ray, infrared spectroscopy, scanning electron microscopy and the chemical analyses by EDS, X­ray fluorescence, atomic absorption, resonant nuclear reaction, ionic cromatography, neutron­activation, ICP and others.

The apatites were more deeply studied and the results of the analyses attested fluorine substitutions by oxidril and chlorine, the phosphate ion by carbonate and the calcium by many cations, emphasizing the rare earth elements which are enriched in the final phases, except for the carbonatitic apatites, originally poorer in these elements. The alteritic profiles are predominatly isalteritic and in some places there are aloteritic formations with dissolution and absolute accumulation zones.

As to the chemical modifications decurrent of weathering, it is possible to verify the mobility of Si, Ca, Na, K and Rb, while Fe, Mn and P tend to accumulate in the alterites.

The hydrothermal action remobilizes the Ca, P, Na and Sr and enriches the hydrothermalized facies with Ba and Fe.

The neoformations of clays with 2:1 and 1:1 types show a partial hydrolysis with mono and bisiallitisation processes and a geochemical alteration of the ferrallitisation "sensu lato" and sialferrallitisation types.

The alteration profiles in Anitápolis are not more developed because the Pinheiros River takes the altered material out of the massif.

ESTUDO ORGANO­PETROGRÁFICO E ORGANO­GEOQUÍMICO DAS FRAÇÕES DE BENEFICIAMENTO DO CARVÃO DA JAZIDA DO FAXINAL, ARROIO DOS RATOS, RS

ORGANIC PETROGRAPHY AND GEOCHEMISTRY OF THE COAL BENEFICIATION FRACTIONS OF THE FAXINAL COALFIELD, ARROIO DOS RATOS, RS

Gerson Luís Miltzarek (1991)

Adviser: Zuleika C. Corrêa da Silva

Abstract

The results of petrographic and geochemical studies of the coals from the Faxinal Coal Field, Arroio dos Ratos, RS, are presented. The analyzed samples were obtained from the washery at the Faxinal Mine, where they underwent two beneficiation process: Jigging and Sink­Float.

The petrographic study comprised vitrinite reflectance measurements, maceral, microlithotype and mineral determinations, proximate analysis (including ash, volatile matter, moisture and fixed carbon), sulfur and calorific value determiantions.

The geochemical analysis comprised total organic carbon determination, pyrolisis, extractable organic matter, liquid and gas chromatograpahic separation, terpane, esterane and stable carbons isotopes.

The coals present a predominance of vitrinite and inertinite over liptinite. Vitrinite tends to concentrate on the lower density fractions, whereas inertinite and minerals concentrate on the higher density fractions. The amount of minerals increass with increasing density. Liptinite concentrate on the fractions +1.5­1.6 g/cm³ of the ROM coal, the washed coals (CE 4,700 and CE 3,100) and of the refuses, and on the fractions +1.7­1.8 g/cm³ of the washed coals.

The variation on organic matter (vitrinite + inertinite + liptinite) of the ROM coal and the fractions of material not exceeding 0.5mm in diameter controls the volatile matter, moisture and calorific value, whereas ash content is controlled by the content of minerals.

The contents of ash and mineral matter tend to increase on the higher density fractions, as opposed to organic matter, volatiles, calorific value and moisture, which concentrate on the lower density fractions.

The values of reflectance on ROM coal and jigging products had no significant change, what indicates the little influence of reduction of minerals in the reflectance of vitrinite in these fractions.

Integrated data of the different geochemical methods show the organic matter to be of low grade of coalification and of woody­plant origin. The extract composition demonstrates the organic matter to be of mixed type and highly influenced by algae and bacteria.

Gas chromatographic separation data show that paraffins present up to thirty carbon numbers, a high pristane/phytane ratio, and bimodal chromatograms, also suggesting a woody­plant origin influenced both by algae and bacteria.

The organic matter is also show to be of low grade of coalification by the final temperature of pyrolisis (less than 440°C), the small number of hydrocarbons, low values of (EO/COT), carbon preference index (CPI) different from 1.0, high P/n­C17 and F/n­C18 rations, thepresence of less stable compounds, and the low values of C31 (22S/22R) and C32 (22S/22R).

In order to choose the correct method of beneficiation it is necessary to consider two main factors: the use of the beneficiated coal and the economical aspect. The detailed study of the samples which underwent the Jigging and the Sink­Float Beneficiation Processes is an auxiliary tool.

PETROLOGIA E GEOQUÍMICA DO COMPLEXO BÁSICO DE LOMBA GRANDE, RS

PETROLOGY AND GEOCHEMISTRY OF THE LOMBA GRANDE BASIC COMPLEX, RS

Antônio Pedro Viero (1991)

Adviser: Ari Roisenberg

Abstract

The Lomba Grande Basic Complex is located in the Gravataí district, RS, and formed by three hypabyssal bodies, informally named Olivine­gabro, Shell­dolerite and Oriental Dolerite, intruded in the sedimentary rocks of the Botucatu and Sanga do Cabral Formations. The Olivine­gabro constitutes more than 95% of the Complex total volume; it is an irregular body with approximately 0.47km³ and with an actual thickness up to 480m. It is relatively primitive in character, with high concentrations of MgO, Cr, Ni and Co, low concentrations of incompatible elements (K, Rb, Ba, Zr and REE), and a transitional affinity. The REE pattern is similar to the P­MORB pattern, with low fractionation (LaN/YbN~4,3) and without negative anomaly of Eu (Eu/Eu*~0,83). The K­Ar ages are of approximately 160 Ma (Late Triassic), what is similar to the early volcanic activities of the Paraná Basin. The chilled margin (MgO~11%) suggests that the magmatic liquid is derived from a picritic magma by crystal fractionation processes at a pressure of 10 Kb. The evolution of the magmatic chamber comprises a combination of replenishment with magmatic differentiation processes. The latter, probably, occur by olivine and plagioclase frac-tionation, which produces segretation of a residual liquid by convective movements.

The shell­Dolerite envelopes partially the Olivine­gabro and presents K­Ar ages of approximately 120 Ma. It is formed by two types of dolerites, chemically similar to the low­TiO2 volcanic rocks of the Paraná Basin (TiO2 < 1.54; MgO = 3.0 to 6.5%; low concentrations of incompatible elements). The REE pattern presents low fractionation (LaN/YbN~5.) and a discreet negative anomaly of Eu (Eu/Eu*~0.7). The parental liquids are probably originated by crystal fractionation processes of a picritic magma, with a low degree of upper crust assimilation.

The Oriental Dolerite is a small body formed by an olivine dolerite and a non­olivine dolerite, with K­Ar ages of approximately 125 Ma. The former presents the highest MgO, Cr and Ni contents. The contents of TiO2 and incompatible elements are similar to the low­TiO2 volcanic rocks of the Paraná Basin.

The REE pattern presents a low fractionation (LaN/YbN~5.1) and a discreet negative anomaly of Eu (Eu/Eu*~0.7).

EVOLUÇÃO CINEMÁTICA DO CINTURÃO DOM FELICIANO DURANTE O CICLO BRASILIANO

KINEMATIC EVOLUTION OF THE DOM FELICIANO BELT DURING THE BRASILIANO CYCLE

Andréa Tommasi (1991)

Adviser: Luís Alberto D'Ávila Fernandes

Abstract

Kinematic analysis of key areas in the Southern Brazilian portion of the Brasiliano/Pan­Africano Dom Feliciano belt supported the establishment of the approximate evolution of the bulk displacement field for the orogen. The obtained kinematic pattern can be used to constrain geodynamic interpretations of this orogen.

Four key areas were selected as representative of the main lithotectonic assemblages of the Dom Feliciano belt, based on a preliminary tectonic model of a two­stage collision between the Rio de La Plata and Kalahari cratons (Tommasi & Fernandes 1990). This model consists of:

1. Collision between the Kalahari craton and an early magmatic association (AAM I) produced on the eastern margin of the Rio de La Plata craton by westward subduction of a Proto­Atlantic Ocean, resulting in the crustal thickenning of these units.

2. This early collision has induced the closure of the back­arc basin, causing the development of a late magmatic association (AAM II). This convergence ended by the collision between the Kalahari craton - AAM I assemblage and the Rio de La Plata craton, promoting the tectonic incorporation of ophiolites (?) into the continental crust (AOM).

The orogen­parallel lithotectonic assemblages formed by this convergence consist of:

1. a "Magmatic Arc Assemblage I" (AAM I), typified by the earlier granitoids (orthogneisses and migmatites) of the Pelotas Batholith (sensu Fragoso Cesar et al. 1986), studied in the Quitéria­Capivarita and Piratini key areas;

2. a deformed back­arc basin, the "Marginal Basin Assemblage" (ABM) - cropping out in the Santana da Boa Vista key area;

3. an "Ophiolite­mélange Assemblage" (AOM), corresponding to the volcano­sedimentary and ultramaphic sequences of the western part of the Sul­riograndense Shield;

4. a "Magmatic Arc Assemblage II" (AAM II), represented by the calc­alkaline magmatic association cropping out in the western Sul­riograndense Shield, both (AOM & AAM II) registered in Lavras key area and;

5. syn­collisional granites, which were emplaced during the orogen­parallel movement in the AAM I and ABM.

In the AAM I, km­thick, flat­ ­lying mylonitic sequences with an E­W stretching lineation affecting orthogneisses and migmatites, under upper to middle amphibolite facies metamorphic conditions, were cut by NE­oriented strike­slip shear zones of upper amphibolite to middle/lower greenschist facies. This strike­slip deformation was mostly accommodated along two syntectonic granitic batholiths of calc­alkaline and peraluminous compositions in the Quitéria­Capivarita key area, whereas in the Piratini key area an extensive reworking of migmatites was observed. Thus, the kinematic evolution of the AAM I is characterized by an early tectonic transport transverse to the length of the belt along flat­lying shear zones (probably related to a crustal thickening episode), that is followed by an orogen­parallel movement along strike­slip shear zones with an important associated magmatism.

The kinematic pattern of the AOM is specially well exposed in the Santana da Boa Vista key area. In this area, a periclinal structure resulting from late­stage folding puts in evidence flat­lying shear zones with NE­oriented stretching lineations that promoted the tectonic interleaving of supracrustal rocks with sheet­like granites and gneisses of the Transamazonian basement under upper amphibolite to greenschist facies metamorphic conditions. Therefore, the deformation in the ABM was dominated by orogen­parallel movement along flat­lying mid­crustal shear zones.

In the Lavras key area (AOM & AAM II), a calc­alkaline magmatic association (diorites, tonalites and trondhjemites) tectonically interleaved with peridotites (harzburgites) was recognized. The retrogression of the harzburgites to serpentinites and Mg­schists showing a flat­lying foliation characterizes the lowest metamorphic conditions of the shearing event (amphibolite facies), while an E W­oriented mineral lineation (pyroxenes) and a sub­horizontal banding within more preserved lenses of harzburgites suggest an early high temperature (~900°C) lithospheric flow showing the same kinematic pattern for these rocks. These structures are reoriented next to NE SW and NW SE­oriented strike­slip shear zones functionning under greenschist metamorphic conditions. Thus, the kinematic pattern in the AOM & AAM II is characterized by high­tempe-rature flow transverse to the belt, developed under decreasing metamorphic conditions, followed by movement in strike­slip shear zones parallel and at high­angle to the belt.

Therefore, the kinematic evolution of the Dom Feliciano belt has started with a tectonic flow transverse to the belt under metamorphic conditions of upper to middle amphibolite facies, recognized only in the AAM I and probably associated to crustal thickenning in this assemblage. This event was followed by partitionning of the deformation in orogen­parallel motions in the eastern, more internal domains of the belt and orogen transverse motions in western, more external domains. This orogen­parallel flow, developed under amphibolite to greenschist facies metamorphic conditions, was further partitionned in high (in the AMM I) and low angle shear zones (in the ABM).

Based on the evolution of kinematic pattern of the Dom Feliciano Belt, the following preliminary geodynamical inferences can be made:

1. The belt was formed by a collisional process between two continental plates: the Kalahari and Rio de La Plata Cratons, that had a high (ca.90°) initial angle of convergence. This is suggested by the record of early movements transverse to the belt with no orogen­parallel movements associated.

2. The transition of an orogen­ ­transverse to an orogen­parallel motions regime in the late stages of the tectonic evolution of the eastern, more internal domains of the belt, suggests the effect of changes introduced in the mechanical system during its evolution, as the development of heterogeneities parallel to the plate limits induced by the convergence process itself (magmatic arcs, marginal basin ...), or an increase in the importance of the buoyancy forces due to the early crustal thickenning preventing further orogen­transverse displacements.

3. The partitionning of the oro-gen­parallel motions in high and low­angle shear zones suggests a transgressional regime for this deformation.

Thus, the kinematic analysis can place some constraints on the geodynamic interpretations that, if integrated with data from other branches of the Earth Sciences, can be used to build a sound geodynamical model for the Brasiliano/Pan­African evolution of the Dom Feliciano belt.

PETROLOGIA E GEOQUÍMICA DO VULCANISMO MESOZÓICO DA BACIA DO PARANÁ NA REGIÃO OCIDENTAL DO RIO GRANDE DO SUL E SANTA CATARINA

PETROLOGY AND GEOCHEMISTRY OF THE MESOZOIC VOLCANISM OF THE PARANÁ BASIN IN WESTERN RIO GRANDE DO SUL AND SANTA CATARINA

Jaqueline Ozório Chies (1991)

Adviser: Ari Roisenberg

Abstract

The Mesozoic magmatism of the Paraná Basin is essentially represented in the western region of Rio Grande do Sul and Santa Catarina by a sequence of basalts to basaltic traqui­andesites, which are dominant in area and volume. Porphyritic dacites and traquidacites (Chapecó type), and aphyric dacites and riolites (Palmas type) are also found in the volcanic sequence. A rheoignimbritic origin for the acidic volcanics is indicated by the presence of tuffaceous textures, and banded and brecciated structures in these rocks. The statistical treatment of chemical data differentiates three groups of basic and intermediate volcanics. One of these groups is relatively enriched in TiO2, P2O5, Sr, Ba, Zr, La e Ce. Another set of samples has the greatest values of Cr and Ni, and the smallest concentrations of La, Ce and Y. The third set shows the lowest values of Sr and Zr, and the highest concentrations of SiO2. The acidic volcanics are also separated into three statistical groups. One of these sets (Palmas type) is characterized by a relative enrichment in SiO2, Rb and Cu, and the lowest values of TiO2, MnO, MgO, CaO, Na2O, P2O5, Ba, Sr and Zr. The other two groups (Chapecó type) are discriminated by Na2O, P2O5 and Zr concentrations. The enrichment factor of the high­TiO2 basalts trace element ratios relative to the low­TiO2 ones indicates a generation by melting of garnet­peridotitic residual (14­17%) or initial (12­15%) mantles for the high­TiO2 basic volcanics. Considering the same source compositions, the low­TiO2 basalts may be produced by melting degrees higher than 20%. Mathematic modelling based on trace element mantle concentrations for a particular set of low­TiO2 basalts points out to an origin from a lherzolitic source by melting degrees between 10 and 15%. Fractional crystallization and simple crustal assimilation processes may not be involved in the acidic and intermediate rocks petrogenesis. A mathematic model that combines crustal assimilation with a maximum of 20% basic magma crystal fractionation at a crystallization rate five times higher than the assimilation rate is compatible with the generation of the low and high­TiO2 intermediate rocks. The assimilated material belongs to the upper crust or to a mixture of crustal material in the first case, while the lower crust may be involved in order to produce the high­TiO2 intermediate volcanics. A parental magma of the same statistical group is considered in each situation.

The Chapecó acidic volcanics seem to be generated from the lower crust by melting degrees between 10 and 15%. The Palmas dacites and riolites petrogenesis is compatible with 10 to 20% melting of an heterogeneous crustal source represented by the bulk crust average.

PETROLOGIA E LITOQUÍMICA DE UMA PARCELA DA SEQÜÊNCIA VULCANO­SEDIMENTAR DO COMPLEXO METAMÓRFICO BRUSQUE NA REGIÃO DO RIBEIRÃO DO OURO, SC

PETROLOGY AND LITHOCHEMISTRY OF A PART OF THE VOLCANO­SEDIMENTARY SEQUENCE BELONGING TO THE BRUSQUE METAMORPHIC COMPLEX IN THE REGION OF RIBEIRÃO DO OURO, SC

Andrea Sander (1992)

Adviser: Léo Afrâneo Hartmann

Abstract

This dissertation deals with the main petrologic and lithochemical aspects of part of the vulcano­sedimentary sequence of the Brusque Metamorphic Complex, in Ribeirão do Ouro region, Santa Catarina State, with special emphasis on its metabasic and meta­ultrabasic rocks.

The primary structures preserved in the lithotypes of sedimentary or igneous origin of this Sequence, together with petrographic criteria, allowed to individualize and to map four different lithofacies units, named as their protoliths: 1) Pelitic­Arenaceous Siliciclastic Unit; 2) Arenaceous Siliciclastic Unit; 3) Carbonaceous Unit; and 4) Volcanogenic Unit.

A lithochemical study was performed only in respect to the Volcanogenic Unit, whose chemical variations show two different populations: a) a high­MgO and low­alkalic one, formed by metagabros, porphyritic metabasic rocks and magnesian schists; b) a low­MgO and high­alkalic one, constituted of metabasalts and variolitic metabasalts. The lithochemical characteristics of these rocks suggest that they came from only one magmatic source, with a transitional nature between tholeiitic and alkaline magmas, compatible with a vulcanic mid­plate regime.

The petrographic and lithochemical studies revealed that the circular structures of the variolitic metabasalts in the Vulcanogenic Unit were formed by fast cooling and consequent fractionation of the spherulitic quartz and albite.

The integration of the field, petrographic and lithochemical data led to the paleoenvironmental interpretation of the facies units and to the working up of a depositional model related to platform and submarine fan deposits.

ESTUDO DA ALTERAÇÃO DO ANORTOSITO CAPIVARITA­RS: EVOLUÇÃO MINERALÓGICA E GEOQUÍMICA

STUDY OF THE ALTERATION OF THE CAPIVARITA ANORTHOSITE - RS: MINERALOGICAL AND GEOCHEMICAL EVOLUTION

Flávia Schenato (1992)

Adviser: Milton Luiz Laquintinie Formoso

Abstract

The Capivarita Anorthosite, located to the northwest of the Pelotas Batholite of the Dom Feliciano Belt, constitutes a massif of metanorthositic rocks associated with polydeformed rocks in crustal­scale shear zones, at high grade metamorphic conditions. Microstructural evidences of crystalline plasticity mechanisms show that dynamic recrystallization has occurred under upper amphibolite facies conditions.

Younger granitic intrusions in the metanorthosite are responsible for the partial tectonic uplift of the area and for non­extensive hydrothermal activity, related to solution diffusion in rock­to­open spaces (joints, veins, etc.) direction.

Intense activity of descending superficial solutions, in the uplifted zones near granite­metanorthosite contact, resulted in the formation of large kaolin deposits of residualtype, where rock is homogeneously altered to kaolinite.

Structural and mineralogical transformations near the intrusions mark the evolution of a primary mineralogy (plagioclases, amphiboles) to a secondary mineral assemblage constituted essentially by haloisites (7­10Å) and kaolinites. Mineralogical (crystallinity, morphology and texture) and chemical (Fe+3 - kaolinites) features of kaolinite are comparable to those of kaolinites crystallized in supergenic conditions.

Primary mineral transformations of rocks localized in flat and distal (from the intrusion) areas present distinct evolutionary features marked by incipient alteration, where pseudomorphic crystallizations (di and trioctaedral vermiculites, smectites and kaolinites) are directly influenced by the nature of the primary minerals.

PETROGRAFIA E LITOQUÍMICA DO MONZOGRANITO SANTO ANTONIO - DOM PEDRITO, RS

PETROGRAPHY AND LITHOCHEMISTRY OF THE SANTO ANTONIO MONZOGRANITE - DOM PEDRITO, RS

Carla Ennes de Barros (1992)

Adviser: Lauro Valentim Stoll Nardi

Abstract

The Santo Antônio Monzogranite is an eliptically­shaped body of approximately 30km² surface area, with is major axis oriented NW­SE. It exhibits intrusive contacts with the Santa Maria Chico Granulitic Complex and with the volcanic rocks of Hilario Formation. Dominant rock types are monzogranites, with minor amounts of quartz monzonites, quartz monzodiorites and granodiorites. The mineralogy is plagioclase (An25­35), alkali­feldspar, quartz, magnesium­hornblende, salitic­augite, biotite, titaniferous­magnetite, apatite, zircon and sphene. Three textural facies were identified: equigranular, medium - porphyrytic and fine - porphyritic. The crystallization of these rocks occurred under pressures lower than 1Kb, and the maindifferentiation process was that of mineral fractionation. The geochemical characteristics of the Santo Antônio Monzogranite, mainly the SiO2 × (Na2O+K2O) relation, associated with its potassic character, allows its identification as a member of the shoshonitic series. Furthermore, the high contents of Ba and Sr, together with moderate values of Zr, LREE, TiO2, and P2O5, support such classification. This monzogranite was generated at the final stages of the Brasiliano Orogeny, presenting an age (Rb­Sr) of 645 Ma. and initial ratio of 0.70462. Its petrological and geochemical characteristics permit to include it in the Lavras do Sul Shoshonitic Association.

DAS MINAS DE COBRE E CARVÃO AO MODELO DE COLISÃO CONTINENTAL: CONTRIBUIÇÃO AO ESTUDO DA MUTAÇÃO EPISTEMOLÓGICA DOS MODELOS DO PRÉ­CAMBRIANO DO ESCUDO SUL­RIO­GRANDENSE (1823 A 1990)

FROM THE COPPER AND COAL MINES TO THE MODEL OF CONTINENTAL COLLISION: A CONTRIBUTION TO THE STUDY OF THE EPISTEMOLOGICAL MUTATION OF THE MODELS FOR THE PRE­CAMBRIAN OF THE SUL­RIO­GRANDENSE SHIELD (1823 TO 1990)

Rualdo Menegat (1992)

Adviser: Luís Alberto D'Ávila Fernandes

Abstract

In this dissertation the results of an epistemological analysis of mutations suffered by geological models proposed for the Pre­Cambrian Sul­Rio­Grandense Shield between 1825 and 1990 are reported. After an introductory discussion of epistemological concepts, the nature and status of a research program or geological epistemology was evaluated under the light of the New Epistemology. This possibility was traduced by the heuristic simulation of a geological research program in terms of the Black­box Problem, through which the main characteristics of a scientific problem become clear and the classical methods of science (neutrality of observation, existence of an unique method, the inductivistic logic, the concept of cumulative knowledge, and the absence of a close relationship between subject and object of science) can be refuted. The deductivist and inductivist logic as well as falseability and verificability can thus be contrasted. The concepts of paradigm and research program are enunciated in terms of the consistency between model, theory of object, methods and the relations between paradigm and cosmovision, bringing into evidence the relationships between subject and object of science. The second part of this work is a historical account on the evolutionary models for the Rio Grande do Sul Shield, taking into account their epistemological characteristics, and specially trying to identify in each research program its core and protective belts (models). Five different periods were recognized: (i) the NATURALISTIC (1825­1908), represented by Smith's model; (ii) the GEOGNOSTIC­MINING (1909­1940), represented by Carvalho's model, during which the first scientific test of the Continental Drift theory was undertaken by Du Toit's model; (iii) the EPIROGENIC­MINING (1941­1958), represented by Leinz's and Beurlen­Martins' models; (iv) the GEOSSINCLINE­METASSOMATIST (1959­1977), represented by Picada­Tessari's model; and (v) the PLATE TECTONICS (from 1978 onwards), represented by Ribeiro's, Fragoso­César's and Tommasi­Fernandes' models. Each of these models were identified in terms of the composing elements of the research program which has permitted the recognition of four principal epistemological mutations. These could be enunciated according to their methodological nature. The change in models can result from significant shifts of the core of the research program or as a function of different emphasis of its protective belt. It was possible to demonstrate that (i) no research program was totally overcome; (ii) there were mixtures of some elements of protection belts of different research programs; (iii) no mutation of the type 'complete rupture' was verified; (iv) Du Toit's model was an epistemological singularity during the geognostic­mining period and, although it has not promoted an epistemological revolution in Kuhn's sense, it promoted the renaissance of the geological research program; (v) there was a rationality of the epistemological mutations guided by a progressive realization of the time represented by the record, which was made possible as long as the recognition of the relations of sucession between several registers and processes, previously regarded as local or fragmentary, has obliged to consider them in a regional scale so that they could also be integrated to latter analyses. The consequent identification of hierarchies in the geological record has made complex their correlation in terms of their synchronous/diachronous nature, in such a way that it could only be possible as long as the sucession of processes responsible for the record could be established. Considering the spatial limits (the Earth), such processes had to be placed in terms of the hierarchy of global chrono­geodynamical systems, according which the depth of time could be perceived as far as its factorization could be given, according to a hierarchy of processes with which the hierarchy of registers could be correlated; (vi) that through the identification of the role played by discontinuities (faults in special) in the geological record, it was permitted to recognize the relative ages of development of geological processes (in increasing scale and complexity) putting into evidence the need for compatibility between tectonic theory and the stratigraphical record during each analyzed historical period; (vii) and that the construction of geologic object implies that global process of one period become local in the following and vice­versa; and, i.e., when the record was regarded as regional, another relationship of the compartimentation of space can be established so that a new global process is then necessary to explain the new configuration. Thus, the old compartimentation becomes just part of the new one in such a way that the global process that previously explained it, now is valid only for this part.

CARACTERIZAÇÃO DAS CONDIÇÕES DE FLUXO EM UMA ZONA DE CISALHAMENTO TANGENCIAL NA REGIÃO DE SANTANA DA BOA VISTA (RS)

CHARACTERIZATION OF THE FLOW CONDITIONS AT A TANGENTIAL SHEAR ZONE IN THE SANTANA DA BOA VISTA REGION (RS)

Carla Cristina Porcher (1992)

Adviser: Luís Alberto D'Ávila Fernandes

Abstract

Tectonic interleaving of Lower Proterozoic (Eburnian) sialic basement and a metavolcano­sedimentary sequence of Upper Proterozoic age (Brasiliano Cycle) was recognized in the western part of the Dom Feliciano Belt, Santana da Boa Vista region. The trondhjemitc­tonalitic gneisses (Encantadas gneisses) and intrusive granites of the basement, as well as the supracrustal rocks belonging to the marginal basin sequence, were deformed along a thick flat­lying shear zone responsible for their tectonic intercalation. This structure was recognized on the basis of characteristics of developed tectonites showing widespread grain­size reduction and the non­homogeneous and non­coaxial nature of the deformation. During late stages of structural evolution of these rocks, a regional ­ scale NE - periclinal antiform, which controls the outcrop pattern, was developed.

Each lithostructural unit affected by the shear zone presents a typical association of mesoscopic and microscopic­scale structures, which permit to characterize the tectonic flow regarding its kinematics and rheologic behavior, as well as the thermal history of deformation. The attitude of pervasive planar structures that characterize the fabric indicates that the shearing­plane was sub­horizontal with a NE­SW transport direction (if the effects of late folds are subtracted). Through the analysis of kinematic indicators of several types and scales (mainly microscopic) it was possible to demonstrate a top to NE transport sense of movement for the upper block. Amphibolite to green schist syntectonic retrogressive metamorphic conditions were inferred from microstructures and parageneses in the deformed quartzofeldspatic and metasedimentary rocks, respectively.

Structural correlation of this flat­lying shear zone with other similar structures of the Dom Feliciano Belt was established mainly on the bases of their kinematic evolution, since the radiometric data obtained in this work do not reflect the age of deformation. The data obtained, however, have allowed the preliminary recognition of the mylonitized granitoids as a part of the Early­Proterozoic basement.

Taking into account the direction and the sense of tectonic flow, thermal history of deformation and the radiometric data it was possible to conclude that: (i) the flat­lying shear zone described in Santana da Boa Vista region can be extended further south (until Cerro dos Porongos region), being recognized as one of the most important mid­crustal movement zone of the Dom Feliciano Belt and if (ii) it's synchroneity with the strike­slip Dorsal de Canguçú (to the east) and Caçapava do Sul flat­lying (to the west) shear zones can be demonstrated, they could represent an important tectonic event with belt­parallel tectonic transport ('K2' - Fernandes et al. 1992).

Although the geodynamic meaning of the belt­parallel movements in tectonics belts is still not well understood, the increasing recognition of events as such in deformation belts suggests that it is a dominant mode of deformation in Phanerozoic and Upper Precambrian orogenic zones (Vauchez & Nicolas 1991). The comparative analysis between the models proposed for well­known orogens and the Dom Feliciano Belt has allowed speculations about the role played by the flat­lying Santana da Boa Vista shear zone during the belt­parallel K2 deformation.

GEOCRONOLOGIA POR TRAÇOS DE FISSÃO DE MACIÇOS ALCALINOS DO BRASIL MERIDIONAL

GEOCHRONOLOGY OF ALKALINE MASSIFS FROM SOUTHERN BRAZIL BY MEANS OF THE FISSION TRACK METHOD

Ricardo Baitelli (1992)

Adviser: Enio Soliani Júnior

Abstract

This dissertation presents 24 ages carried out by Fission Track Method on samples from Piratini (RS), Lages and Anitápolis (SC), Tunas (PR) and Jacupiranga (SP) alkaline massifs.

The Anitápolis Massif has the majority of age determinations (15), and revealed to be multi­episodic: at least four igneous phases were detected through the corrected ages to 130°C isotherm. The first one, about 200 Ma, was correlated to a phase of Jacupiranga Complex, whose age was the oldest one. The subsequent igneous episode ranged from 160 to 150 Ma; the third one registered at Anitápolis, between 140 and 130 Ma, exhibits ages that are concordant with those of Piratini and Tunas massifs; on the other hand, the youngest magmatic phase settled between 120 and 100 Ma is also represented by a similar result found still at Tunas Complex. From all those studied regions, Lages provided the most recent results, about 90­80 Ma.

The fission track ages were in good agreement with values obtained by others isotope systems (K­Ar and Rb­Sr).

The projected track length measurements allowed to outline the thermal history from the studied massifs. It has been recognized a continuous cooling process to the Anitápolis, Lages and Jacupiranga complexes and an acceleration in the cooling rate to the Piratini and Tunas massifs. Besides their temporal correlation, it can also be noticed that the cooling pattern of Piratini, Anitápolis and Tunas revealed a similar behaviour. The Lages and Jacupiranga complexes were submitted to different cooling histories from the others and they are also distinct between themselves.

Considering that the main purpose of this work was achieved, i.e., to verify the applicability of the Fission Track Method on rocks such as founded at the alkaline massifs from Southern Brazil, we suggest the application of this methodology on other alkaline regions and the retaking of the studies in the same bodies here analyzed to characterize aspects that were only outlined.

CARACTERIZAÇÃO GEOLÓGICA, GEOQUÍMICA E GEOCRONOLÓGICA DA ILHA DEE E PARTE DA ILHA GREENWICH, ARQUIPÉLAGO DAS SHETLAND DO SUL, ANTÁRTICA

GEOLOGICAL, GEOCHEMICAL AND GEOCHRONOLOGICAL CHARACTERIZATION OF THE DEE ISLAND AND PART OF THE GREENWICH ISLAND, SOUTH SHETLAND ARCHIPELAGO, ANTARCTIC

Giles Carriconde Azevedo (1993)

Adviser: Enio Soliani Júnior

Abstract

The different areas studied in this dissertation consist of a volcano­sedimentary association represented by volcanoclastic rocks such as tuffs, lapilli tuffs, breccias and lapilli breccias, epiclastic sediments and intercalated flows which are associated with sub­volcanic rocks of small depth.

The geologic mapping, elaboration of profiles and rock analyses for major oxides, trace elements and REE, associated with 24 new K­Ar ages and initial ratio of Sr87/Sr86, obtained by this study, permitted the characterization of some lithostratigraphic units and their correlations to other areas of the South Shetland Islands. The K­Ar and Rb­Sr ages previously obtained for the region were also reviewed.

In N­NE Greenwich Island a volcano­sedimentary association was mapped, Upper Cretaceous in age and correlated to the Coppermine Formation, while in S­SW Middle Crecateous rocks were interpreted as belonging to the Byers Formation. A Lower Tertiary age was attributed to a third volcanic unit, recognized as Fildes Formation. This lava, however, could represent a pre­Tertiary volcanic activity which was later resetted by intrusive events.

The plutonic activity was more intense at the Cretaceous­Tertiary passage and at the onset of the Eocene.

Taking lithogeochemistry into consideration, the different units do not present large compositional variations and consist of basalts, andesitic basalts and rare andesites.

The obtained data show that the rocks from this region of the South Shetland Islands have a tholeiitic character, whereas the younger rocks present a calc­alkaline tendency. It was also possible to notice that the Cretaceous rocks are associated with an arc­island setting or even formed too closely to a trench zone.

CARACTERIZAÇÃO DOS SISTEMAS DEPOSICIONAIS E DAS CAMADAS DE CARVÃO NO PACOTE SEDIMENTAR DA MALHA IV, JAZIDA DE CANDIOTA - RS

CHARACTERIZATION OF THE DEPOSITIONAL SYSTEMS AND COAL­BEARING BEDS OF THE "GRID IV" SEDIMENTARY SEQUENCE, CANDIOTA COAL FIELD - RS

Marcus Vinicius Berao Ade (1993)
Adviser: Zuleika Carreta Corrêa da Silva

Abstract

This dissertation deals with the study of the sedimentary sequence of the Rio Bonito Formation (Lower Permian) at the Candiota Mine, Candiota, Rio Grande do Sul State.

Paleoenvironmental analyses of three lithologicaly distinct intervals were carried out from bottom to top, and considered as fluvial, swamp and barrier island deposits; petrographic analyses - microscopic chemical - of seven seams of the intermediary interval were also developed.

The bottom interval of the Rio Bonito Formation in the area is composed of coarse to conglomeratic sandstones, which were mainly deposited in a fluviatile system. These deposits are overlain by pelitic coal­bearing strata with seven coal seams with interbedded mudstones and shales, which were deposited inswamps protected by a barrier island shoreline. These deposits underlie an interval composed of medium to fine­grained and subordinate coarse­grained quartzarenites, related to a probably transgressive barrier island.

The coal seams of the intermediary intervals are rather thin, less than 1.5m, except the Upper and Lower Candiota seams, with 2.5m each. These coals present high ash content (about 50%) and the microscopic analyses evidenced the predominance of the vitrinite group, except for the "Banco Louco" seam, where macerals of the inertinite group predominate. The Upper and Lower Candiota coal seams were classified as Sub­bituminous A coal or as "Glanz­Braunkohle", according to ASTM and DIN classifications, respectively.